High-Voltage Pulse Ablation Systems and Methods

ABSTRACT

A tissue treatment system configured to ablate a tissue, the system comprising: (a) a clamp assembly comprising a first jaw mechanism and a second jaw mechanism configured to receive and compress a tissue therebetween; (b) a first electrode disposed on the first jaw mechanism and configured to contact the tissue; and (c) a second electrode disposed on the second jaw mechanism and configured to contact the tissue, where the first electrode and the second electrode are configured so that at least one of an ablation energy output of the first electrode and an ablation energy output of the second electrode is automatically adjusted to accommodate variable tissue thicknesses between the first electrode and the second electrode.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. Nonprovisional patentapplication Ser. No. 16/906,979, filed Jun. 19, 2020, which is adivisional of U.S. Nonprovisional patent application Ser. No.14/745,136, filed Jun. 19, 2015, which is a continuation of U.S.Nonprovisional patent application Ser. No. 13/149,687, filed May 31,2011, the entire content of which is incorporated herein by referencefor all purposes. This application is related to U.S. Pat. Nos.6,369,465, 6,428,537, and 6,679,269, the disclosures of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

Embodiments of the present invention related generally to the field ofmedical devices and methods, and in particular to therapeutic modalitiesinvolving tissue ablation or lesion formation.

Atrial fibrillation (AF) can refer to a heart beat rhythm disorder (or“cardiac arrhythmia”) in which the upper chambers of the heart known asthe atria quiver rapidly instead of beating in a steady rhythm. Thisrapid quivering reduces the heart's ability to properly function as apump. AF is a common clinical condition, and presents a substantialmedical issue to aging populations. AF is costly to health systems, andcan cause complications such as thrombo-embolism, heart failure,electrical and structural remodeling of the heart, and even death.Relatedly, AF typically increases the risk of acquiring a number ofpotentially deadly complications, including thrombo-embolic stroke,dilated cardiomyopathy, and congestive heart failure. Quality of life isalso impaired by common AF symptoms such as palpitations, chest pain,dyspnea, fatigue and dizziness. People with AF have, on average, afive-fold increase in morbidity and a two-fold increase in mortalitycompared to people with normal sinus rhythm. One of every six strokes inthe U.S. (some 120,000 per year) occurs in patients with AF, and thecondition is responsible for one-third of all hospitalizations relatedto cardiac rhythm disturbances (over 360,000 per year), resulting inbillions of dollars in annual healthcare expenditures. The likelihood ofdeveloping AF increases dramatically as people age; the disorder isfound in about 1% of the adult population as a whole, and in about 6% ofthose over age 60. By age 80, about 9% of people (one in 11) will haveAF. According to a recent statistical analysis, the prevalence of AF inthe U.S. will more than double by the year 2050, as the proportion ofelderly increases. A recent study called The Anticoagulation and RiskFactors in Atrial Fibrillation (ATRIA) study, published in the Spring of2001 in the Journal of the American Medical Association (JAMA), foundthat 2.3 million U.S. adults currently have AF and this number is likelyto increase over the next 50 years to more than 5.6 million, more thanhalf of whom will be age 80 or over.

As the prevalence of AF increases, so will the number of people whodevelop debilitating or life-threatening complications, such as stroke.According to Framingham Heart Study data, the stroke rate in AF patientsincreases from about 3%/year of those aged 50-59 to more than 7%/year ofthose aged 80 and over. AF is responsible for up to 35% of the strokesthat occur in people older than age 85. Efforts to prevent stroke in AFpatients have so far focused primarily on the use of anticoagulant andantiplatelet drugs, such as warfarin and aspirin. Long-term warfarintherapy is recommended for all AF patients with one or more stroke riskfactors, including all patients over age 75. Studies have shown,however, that warfarin tends to be under-prescribed for AF. Despite thefact that warfarin reduces stroke risk by 60% or more, only 40% ofpatients age 65-74 and 20% of patients over age 80 take the medication,and probably fewer than half are on the correct dosage. Patientcompliance with pharmacological intervention such as warfarin isproblematic, and the drug requires vigilant blood monitoring to reducethe risk of bleeding complications.

More recently, the focus has shifted toward surgical or catheterablation options to treat or effect a cure for AF. The ablationtechniques for producing lines of electrical isolation are now replacingthe so-called Maze procedure. The Maze procedure uses a set oftransmural surgical incisions on the atria to create fibrous scars in aprescribed pattern. This procedure was found to be highly efficaciousbut was associated with a high morbidly rate. The more recent approachof making lines of scar tissue with modern ablation technology hasenabled the electrophysiologist or cardiac surgeon to create the linesof scar tissue more safely. Ideally, re-entrant circuits that perpetuateAF can be interrupted by the connected lines of scar tissue, and thegoal of achieving normal sinus rhythm in the heart may be achieved.

Electrophysiologists often classify AF by the “three Ps”: paroxysmal,persistent, or permanent. Paroxysmal AF, typically characterized bysporadic, usually self-limiting episodes lasting less than 48 hours, isusually the most amenable to treatment, while persistent or permanent AFcan be much more resistant to known therapies. Researchers now know thatAF is a self-perpetuating disease and that abnormal atrial rhythms tendto initiate or trigger more abnormal rhythms. Thus, the more episodes apatient experiences and the longer the episodes last, the less chance ofconverting the heart to a persistent normal rhythm, regardless of thetreatment method.

AF is often characterized by circular waves of electrical impulses thattravel across the atria in a continuous cycle, causing the upperchambers of the heart to quiver rapidly. At least six differentlocations in the atria have been identified where these waves cancirculate, a finding that paved the way for maze-type ablationtherapies. More recently, researchers have identified the pulmonaryveins as perhaps the most common area where AF-triggering foci reside.Triggers for intermittent AF and drivers for permanent AF can be locatedat various places on the heart, such as the atria. For example, wheretriggers or drivers are located near the pulmonary veins, it followsthat treatment may involve electrical isolation of the pulmonary veins.Technologies designed to isolate the pulmonary veins or ablate specificpulmonary foci appear to be very promising and are the focus of much ofthe current research in catheter-based ablation techniques.

There are many instances where it is beneficial to perform a therapeuticintervention in a patient, using a system that is inserted within thepatient's body. One exemplary therapeutic intervention involves theformation of therapeutic lesions in the patient's heart tissue to treatcardiac conditions such as atrial fibrillation, atrial flutter, andarrhythmia. Therapeutic lesions may also be used to treat conditions inother regions of the body including, but not limited to, the prostate,liver, brain, gall bladder, uterus, and other solid organs. Typically,the lesions are formed by ablating tissue with one or more electrodes.For example, certain cardiac surgical procedures involve administeringablative energy to the cardiac tissue in an attempt to create atransmural lesion on the tissue. Although cardiac ablation devices andmethods are currently available and provide real benefits to patients inneed thereof, many advances may still be made to provide improveddevices and methods for creating lesions in cardiac tissue to treat AFand other arrhythmias. Embodiments of the present invention providesolutions to at least some of these outstanding needs.

BRIEF SUMMARY OF THE INVENTION

Embodiments of the present invention provide systems and methods foradministering minimally invasive stand-alone atrial fibrillation therapyusing bipolar clamping technology. Embodiments further encompass veryeffective ablation technologies that provide the flexibility of linearmonopolar devices with the effectiveness of bipolar clamping devices. Insome cases, systems and methods encompass the use of high-voltage pulsesas a non-thermal means of ablating tissue. Embodiments are well suitedfor use with unipolar and bipolar ablation techniques, and encompasstreatments involving box lesions and conduction block, as well as theadministration of tissue stunning protocols.

High-voltage pulses applied by the electrode eventually kills or ablatesthe tissue to form a lesion. Depending on the procedure, a variety ofdifferent electrophysiology devices may be used to position one or moreelectrodes at the target location. Electrodes can be connected to powersupply lines and, in some instances, the power to the electrodes can becontrolled on an electrode-by-electrode basis. Examples ofelectrophysiology devices include catheters, surgical probes, andclamps. The ablation energy output of individual ablation electrodes canbe automatically adjusted so as to accommodate for variable tissuethicknesses.

In one aspect, embodiments of the present invention encompass methods ofadministering an ablation treatment to a patient that includecompressing a portion of a patient target tissue with a bipolar clampassembly, where the clamp assembly includes a first jaw having a firstelectrode mechanism and a first face and a second jaw having a secondelectrode mechanism and a second face, such that the first jaw face andthe second jaw face are separated by less than about 5 mm. Methods canalso include applying a high voltage pulse regimen to the tissue withthe bipolar clamp ablation assembly. The pulse regimen can provide orinclude a plurality of 500 1000 volt pulses each having a duration ofbetween about 0.02 msec and about 0.1 msec. The pulses can be deliveredat a frequency having a pulse number within a range from about 5 toabout 50 pulses discharged over a time interval within a range fromabout 1 to about 60 seconds. In some instances, the patient tissueincludes a plurality of myocardial cells, and the ablation treatment issufficient to kill the plurality of myocardial cells between the jawfaces. In some instances, the patient tissue includes a plurality ofmyocardial cells, and the ablation treatment is sufficient toirreversible damage the plurality of myocardial cells. In someinstances, the portion of patient tissue includes a strip of tissuebetween the first jaw face and the second jaw face, and the ablationtreatment is sufficient to create a lesion within the strip of tissue,such that the lesion has a maximum width disposed midway between thefirst jaw face and the second jaw face. Optionally, the first jaw facemay include a first electrode having a width of about 2 mm and thesecond jaw face may include a second electrode having a width of about 2mm, and the maximum width of the lesion can be about 10 mm or less.

In another aspect, embodiments of the present invention encompassmethods of administering an ablation treatment to a patient that includeplacing a return pad at a location on the patient's skin, and placing anablation assembly at a patient target tissue, where the ablationassembly includes a first electrode mechanism and a second electrodemechanism. Methods may also include applying a high voltage pulseregimen to the tissue between the first and second electrode mechanismwith the ablation assembly. The pulse regimen may include or provide aplurality of 1000 2000 volt pulses each having a duration of betweenabout 0.02 msec and about 0.1 msec. The pulses can be delivered at afrequency having a pulse number within a range from about 5 to about 50pulses discharged over a time interval within a range from about 1 toabout 60 seconds. In some cases, the patient tissue includes a pluralityof myocardial cells, and the ablation treatment is sufficient to kill atleast a portion of the plurality of myocardial cells located withinabout 5 mm of either of the first electrode mechanism or the secondelectrode mechanism. In some cases, the patient tissue includes aplurality of myocardial cells, and the ablation treatment is sufficientto irreversible damage the plurality of myocardial cells. In some cases,the high voltage pulse regimen includes or provides multiple volt pulseseach having an amplitude of about 1000 volts and a pulse width of about0.05 msec. Optionally, the high voltage pulse regimen can be sufficientto ablate the target tissue to a depth of about 5 mm. In some cases, thehigh voltage pulse regimen includes or provides multiple volt pulseseach having an amplitude of about 2000 volts and a pulse width of about0.05 msec. Optionally, the high voltage pulse regimen can be sufficientto ablate the target tissue to a depth of about 10 mm. In some cases,the tissue has a thickness of about 10 mm and the ablation treatment issufficient to create a lesion within the tissue, where the lesion has asubstantially semicircular cross-section. In some instances, the tissuehas a thickness and the ablation treatment is sufficient to create alesion within the tissue, the lesion having a width of about twice thetissue thickness. In some instances, the tissue includes an atrial walltissue having a thickness of about 4 mm and the ablation treatment issufficient to create a lesion within the tissue, the lesion having awidth of about 8 mm. Optionally, the application of the high voltagepulse regimen may result in little or no cellular damage in thepatient's skin near the return pad. In some cases, the application ofthe high voltage pulse regimen results in a voltage gradient of about10V/cm or lower at the patient's skin near the return pad.

In another aspect, embodiments of the present invention encompassmethods of administering an ablation treatment to a patient that includeplacing a return pad at a location on the patient's skin, and placing anablation assembly at a patient target tissue. The ablation assembly caninclude a first electrode mechanism and a second electrode mechanism,where the first and second electrode mechanisms are spaced more thanabout 2 cm apart. Methods may also involve applying a high voltage pulseregimen to the tissue between the first and second electrode mechanismswith the ablation assembly. The pulse regimen can include or provide aplurality of 1500 3000 volt pulses each having a duration of betweenabout 0.02 msec and about 0.1 msec. In some cases, the patient tissueincludes a plurality of myocardial cells, and the ablation treatment issufficient to kill at least a portion of the plurality of myocardialcells located within about 5 mm of each of the first electrode mechanismand the second electrode mechanism. In some cases, the pulses aredelivered at a frequency having a pulse number within a range from about5 to about 50 pulses discharged over a time interval within a range fromabout 1 to about 60 seconds. In some cases, the patient tissue includesa plurality of myocardial cells, and the ablation treatment issufficient to irreversible damage the plurality of myocardial cells.Optionally, the high voltage pulse regimen may include or providemultiple volt pulses each having an amplitude of about 1500 volts and apulse width of about 0.05 msec. In some instances, the high voltagepulse regimen is sufficient to ablate the target tissue to a depth ofabout 5 mm. In some instances, the high voltage pulse regimen includesor provides multiple volt pulses each having an amplitude of about 3000volts and a pulse width of about 0.05 msec. Optionally, the high voltagepulse regimen can be sufficient to ablate the target tissue to a depthof about 10 mm. In some cases, the tissue has a thickness of about 10 mmand the ablation treatment is sufficient to create a lesion within thetissue, the lesion comprising a substantially semicircularcross-section. In some cases, the tissue has a thickness and theablation treatment is sufficient to create a lesion within the tissue,the lesion having a width of about twice the tissue thickness. In somecases, the tissue includes an atrial wall tissue having a thickness ofabout 4 mm and the ablation treatment is sufficient to create a lesionwithin the tissue, the lesion having a width of about 8 mm.

In yet another aspect, embodiments of the present invention encompassmethods of administering an ablation treatment to a patient that includeplacing an ablation assembly at a patient target tissue, where theablation assembly includes a first electrode mechanism having a firstelectrode with a first polarity and a second electrode mechanism havinga second electrode with a second polarity opposite the first polarity.The first and second electrode mechanisms can be spaced more than about2 cm apart. Methods may also include applying a high voltage pulseregimen to the tissue between the first and second electrode mechanismswith the ablation assembly, where the pulse regimen includes or providesa plurality of 1000 2000 volt pulses each having a duration of betweenabout 0.02 msec and about 0.1 msec. In some instances, the firstelectrode and the second electrode are similarly sized. In someinstances, the second electrode mechanism includes a plurality of secondelectrodes with a second polarity opposite the first polarity, whereeach of the second electrodes spaced more than about 2 cm from the firstelectrode. In some cases, the patient tissue includes a plurality ofmyocardial cells, and the ablation treatment is sufficient to kill atleast a portion of the plurality of myocardial cells located withinabout 5 mm of the first electrode mechanism. In some cases, the pulsesare delivered at a frequency having a pulse number within a range fromabout 5 to about 50 pulses discharged over a time interval within arange from about 1 to about 60 seconds. In some cases, the patienttissue includes a plurality of myocardial cells, and the ablationtreatment is sufficient to irreversible damage the plurality ofmyocardial cells. In some cases, the high voltage pulse regimen includesor provides multiple volt pulses each having an amplitude of about 1000volts and a pulse width of about 0.05 msec. Optionally, the high voltagepulse regimen can be sufficient to ablate the target tissue to a depthof about 5 mm at the first electrode mechanism. In some cases, the highvoltage pulse regimen includes or provides multiple volt pulses eachhaving an amplitude of about 2000 volts and a pulse width of about 0.05msec. Optionally, the high voltage pulse regimen can be sufficient toablate the target tissue to a depth of about 10 mm at the firstelectrode mechanism. In some instances, the tissue has a thickness ofabout 10 mm and the ablation treatment is sufficient to create a lesionwithin the tissue, where the lesion has a substantially semicircularcross-section. In some instances, the tissue has a thickness and theablation treatment is sufficient to create a lesion within the tissue,where the lesion has a width of about twice the tissue thickness. Insome instances, the tissue includes an atrial wall tissue having athickness of about 4 mm and the ablation treatment is sufficient tocreate a lesion within the tissue, the lesion having a width of about 8mm. Optionally, application of the high voltage pulse regimen can resultin a lesion having a first depth at the first electrode mechanism and asecond depth at the second electrode mechanism, where the second lesiondepth is less than the first lesion depth. Some methods may includeplacing a return pad at a location on the patient's skin.

In still a further aspect, embodiments of the present inventionencompass methods of administering an ablation treatment to a patientthat include placing a return pad at a location on the patient's skin,and placing an ablation assembly at a patient target tissue. Theablation assembly can include a first electrode mechanism and a secondelectrode mechanism, where the first and second electrode mechanisms arespaced at a distance from each other within a range from about 4 mm toabout 10 mm. In some cases, the patient target tissue has a thickness,and the first and second electrode mechanisms are spaced at a distancefrom each other approximately equal to the target tissue thickness. Insome cases, the first electrode mechanism has a first length and thesecond electrode mechanism has a second length, where each of the firstand second lengths are within a range from about 4 mm to about 20 mm.Some methods may include applying a high voltage pulse regimen to thetissue between the first and second electrode mechanisms with theablation assembly, where the pulse regimen includes or provides aplurality of 1500 3000 volt pulses each having a duration of betweenabout 0.02 msec and about 0.1 msec. In some cases, the patient tissueincludes a plurality of myocardial cells, and the ablation treatment issufficient to kill at least a portion of the plurality of myocardialcells located within about 5 mm of each of the first electrode mechanismand the second electrode mechanism. In some cases, the first electrodemechanism can be configured to deliver voltage at a first polarity, andthe second electrode mechanism can be configured to deliver voltage at asecond polarity that is opposite the first polarity. Sources of energycan be configured to provide such voltages to the electrodes. In somecases, the patient target tissue includes an atrial wall. Optionally,the atrial wall can have a thickness of about 4 mm and the first andsecond electrode mechanisms can present or define an edge to edgeseparation distance of about 6 mm. In some cases, the pulses aredelivered at a frequency having a pulse number within a range from about5 to about 50 pulses discharged over a time interval within a range fromabout 1 to about 60 seconds. According to some embodiments, the patienttissue includes a plurality of myocardial cells, and the ablationtreatment is sufficient to irreversible damage the plurality ofmyocardial cells. In some instances, the high voltage pulse regimenincludes or provides multiple volt pulses each having an amplitude ofabout 1500 volts and a pulse width of about 0.05 msec. Optionally, thehigh voltage pulse regimen can be sufficient to ablate the target tissueto a depth of about 5 mm at each of the first electrode mechanism andthe second electrode mechanism. In some instances, the high voltagepulse regimen includes multiple volt pulses each having an amplitude ofabout 3000 volts and a pulse width of about 0.05 msec. In someinstances, the high voltage pulse regimen is sufficient to ablate thetarget tissue to a depth of about 10 mm at each of the first electrodemechanism and the second electrode mechanism. In some instances, thetissue has a thickness of about 10 mm and the ablation treatment issufficient to create a lesion within the tissue, the lesion comprising asubstantially semicircular cross-section. In some instances, the tissuehas a thickness and the ablation treatment is sufficient to create alesion within the tissue, the lesion having a width of about twice thetissue thickness. In some instances, the tissue includes an atrial walltissue having a thickness of about 4 mm and the ablation treatment issufficient to create a lesion within the tissue, the lesion having awidth of about 8 mm.

The above described and many other features and attendant advantages ofembodiments of the present invention will become apparent and furtherunderstood by reference to the following detailed description whenconsidered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B illustrates aspects of a tissue treatment systemaccording to embodiments of the present invention.

FIG. 2 illustrates aspects of a tissue treatment system according toembodiments of the present invention.

FIG. 3 illustrates aspects of a tissue treatment system according toembodiments of the present invention.

FIG. 4 illustrates aspects of a tissue treatment system according toembodiments of the present invention.

FIG. 5 illustrates aspects of a tissue treatment system according toembodiments of the present invention.

FIGS. 6A and 6B illustrates aspects of a tissue treatment systemaccording to embodiments of the present invention.

FIG. 7 illustrates aspects of a tissue treatment system according toembodiments of the present invention.

FIG. 8 illustrates aspects of a tissue treatment system according toembodiments of the present invention.

FIG. 9 illustrates aspects of a tissue treatment system according toembodiments of the present invention.

FIG. 10 illustrates aspects of a tissue treatment system according toembodiments of the present invention.

FIG. 11 illustrates aspects of a tissue treatment system according toembodiments of the present invention.

FIG. 12 illustrates aspects of a tissue treatment system according toembodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Surgical probes which can be used to create lesions often include ahandle, a relatively short shaft that is from 4 inches to 18 inches inlength and either rigid or relatively stiff, and a distal section thatis from 1 inch to 10 inches in length and either malleable or somewhatflexible. One or more electrodes are carried by the distal section.Surgical probes are used in epicardial and endocardial procedures,including open heart procedures and minimally invasive procedures whereaccess to the heart is obtained via a thoracotomy, thoracostomy ormedian sternotomy. Exemplary surgical probes are disclosed in U.S. Pat.No. 6,142,994, the content of which is incorporated herein by reference.

Clamps, which have a pair of opposable clamp members that may be used tohold a bodily structure or a portion thereof, are used in many typessurgical procedures. Lesion-creating electrodes have also been securedto certain types of clamps. Examples of clamps which carry lesioncreating electrodes are discussed in U.S. Provisional Patent ApplicationNo. 61/288,031 filed Dec. 18, 2009 (Attorney Docket No.021063-003400US), U.S. Pat. No. 6,142,994, and U.S. Patent PublicationNos. 2003/0158549, 2004/0059325, and 2004/024175, the contents of whichare incorporated herein by reference. Such clamps can be useful when thephysician intends to position electrodes on opposite sides of a bodystructure in a bipolar arrangement.

Many currently available ablation devices typically use temperatureextremes to create lesions. Most systems apply energy to the targettissue to heat it, and wherever the tissue temperature exceeds about 50°C., myocytes are killed. If cryotherapy probes are used, myocytes arekilled when local temperatures reach temperatures below about −40° C.Whichever ablative device is used, the affected electrically responsivetissue is replaced by non-responsive tissue (scar tissue) which blocksconduction. Thus, energy-based surgical ablative treatments for thetreatment of atrial fibrillation attempt to provide lines of conductionblock in atrial tissue without the need to cut the tissue and sew itback together. The effective ablative treatments create permanentconduction block by the same mechanism as the cut- and sew technique: ascar is eventually formed that forms a line of block across the entirethickness of the atrial wall.

For heat-generating ablation technologies, the size and shape of thelesion created can by defined by the volume of the tissue heated to 50°C. and above. Expressed in another way, the 50° C. isotherm forms theboundary of the lesion created by such technologies. For normothermicpatients, this corresponds to a 13° C. increase in local tissuetemperature. For safety reasons, typically none of the heated tissueshould be heated to above 100° C., since the steam so created candisrupt the tissue, or even cause an atrial wall perforation. Thisconstraint limits both the power levels and power application times forthe energy heating the tissue. In summary, tissue should generally beheated by at least 13° C. to be effective, but safety concerns limitheating to 63° C. for normothermic patients. Since safety is animportant design constraint for ablation devices, this relatively narrowtherapeutically effective window can result in ablation designs that areineffective under some operating conditions. One design strategy thataddresses this issue is to use local surface temperature to controlenergy delivery to the tissue. This strategy can be especially effectivefor ablation technology that creates the hottest tissue temperaturesnear the tissue surface. This approach enables more aggressiveapplications of energy to heat the tissues while avoiding potentiallydangerous overheating situations. The superior results with thetechnology using RF heating with temperature control tend to validatethat approach to ablation device design.

For many heat-generating ablation technologies, the size and shape ofthe lesion created can be determined by both the direct heating patternof the tissue by the ablating device and by passive heat conduction fromthe hotter regions of the directly heated tissue to cooler less stronglyheated regions. Heat conduction usually results in larger lesions thancould be created by heat deposition patterns alone. With the exceptionof bipolar ablation technologies, most heat-generating technologiescurrently on the market have more than a 5 to 1 variation in depositedpower within 2 mm of the tissue surface through which the power enters.For such technologies, lesion dimensions are typically extended wellbeyond 2 mm by heat conduction from tissues heated above 50° C. Althoughlesion growth by heat conduction is generally a much slower process thanthe process of heating tissue directly by tissue absorption of theapplied energy, heat conduction can result in a lesion volume more than10 times larger than would occur by heat deposition alone as long asenergy is applied long enough. However, lesion sizes may be limited whenheat is actively removed into the blood stream. The convective removalof heat at the atrial endocardium can result in a thin region ofsub-endocardial myocardium remaining below 50° C. and thus survivingwhen thermal lesions are applied epicardially. For cryotherapy lesionsapplied to the epicardium, heat conducts from the blood pool into thetissues, resulting in sub-endocardial temperatures remaining abovefreezing and sparing that tissue.

Perhaps the most widely applied technology currently in use for surgicalAF therapy is RF bipolar ablation. Properly designed bipolar ablationdevices can achieve reliable transmural epicardial lesions that isolatepulmonary veins. However, clinical results with this type of technologyoften appear to produce inferior success rates for AF therapy applied topatients with non-paroxysmal AF. In many instances, the technologysuffers from a limited lesion set that can be achieved off bypass andsome versions of the bipolar devices do not appear to create reliableisolation of the pulmonary veins in patients, at least for single ordouble RF power applications. For example, three clinical papers reportthat on average, more than two bipolar RF ablation applications wererequired to achieve acute conduction block of the right pulmonary veinsand more than two bipolar RF ablation applications were required toachieve conduction block in the left pulmonary veins. Embodiments of thepresent invention provide improved ablation systems and methods for thetreatment of atrial fibrillation.

High-voltage pulses can cause dielectric breakdown of the cellularmembrane, resulting in holes being created through those membranes asdescribed in U.S. Pat. Nos. 6,369,465; 6,428,537; and 6,679,269, thecontents of which are incorporated herein by reference for all purposes.The holes can be large enough to enable proteins and even geneticmaterial to flow out of the cells, and prior to resealing sodium andcalcium can rush into the cell and potassium can rush out. Single pulsesstress the cell and can result in stunning. Repeated pulses above about500V/cm reliable kills the myocytes cells; 5-50 such pulses with pulsewidths of 0.01 to 0.1 msec delivered in one minute or less can be lethalto the cells so exposed. Cells exposed to voltage gradients several foldlower than those levels will often be stunned, but will typicallyrecover electrical and mechanical function, with those exposed to thelowest fields recovering faster.

Bipolar Clamp Technologies

For bipolar clamp ablation technologies, the system can be configured sothat electrodes on the facing jaw faces are separated by less than about5 mm after compressing the tissues between the jaw faces. In such aconfiguration, voltage pulses of 500-1000 volts applied between the jawfaces using pulse durations of 0.02-0.1 msec are in most instancessufficient to kill all myocardial cells between the jaw faces. When itis desired that all or substantially all of the myocardial cells beirreversibly damaged by the high voltage gradients within the targetedtissue, 10-50 pulses can be delivered over a 1 to 60 second timeinterval. For bipolar clamping technologies, the region of tissuesubjected to the very high voltage field is usually limited to arelatively narrow strip of tissue between the jaws, with the lesionwidth being widest midway between the jaws. For 2 mm wide electrodes,for example, the maximum lesion width is usually 10 mm or less.

Turning now to the drawings, FIG. 1A illustrates aspects of a treatmentsystem 100 a according to embodiments of the present invention.Treatment system 100 a includes a clamp assembly 110 a, an actuatorassembly 120 a, and a coupling assembly 130 a in operative associationwith both the clamp assembly and the actuator assembly. Clamp assembly110 a includes a first jaw mechanism 112 a and a second jaw mechanism114 a. Coupling assembly 130 a may include a shaft or other elongatemember that allows the physician or operator to access or reach asurgical site with the clamp assembly, when the physician is holdingactuator assembly 120 a. Coupling assembly 130 a includes a proximal end132 a and a distal end 134 a. As shown here, clamp assembly 110 a iscoupled with distal end 134 a of coupling assembly 130 a, and actuatorassembly 120 a is coupled with proximal end 132 a of coupling assembly130 a. Clamp assembly 110 a is depicted in a generally closedconfiguration, such that first jaw mechanism 112 a contacts or issituated near second jaw mechanism 114 a. In some cases, a treatmentsystem may present a disposable dedicated bipolar clamp havingsingle-position jaws and a symmetric jaw-release on a plunger stylebody.

FIG. 1B illustrates aspects of a treatment system 100 b according toembodiments of the present invention. Treatment system 100 b includes aclamp assembly 100 b, an actuator assembly 120 b, and a couplingassembly 130 b in operative association with both the clamp assembly andthe actuator assembly. Clamp assembly 100 b includes a first jawmechanism 112 b and a second jaw mechanism 114 b. Coupling assembly 130b may include a shaft or other elongate member that allows the physicianor operator to access or reach a surgical site with the clamp assembly,when the physician is holding actuator assembly 120 b. Coupling assembly130 b includes a proximal end 132 b and a distal end 134 b. As shownhere, clamp assembly 100 b is coupled with distal end 134 b of couplingassembly 130 b, and actuator assembly 120 b is coupled with proximal end132 b of coupling assembly 130 b. Clamp assembly 100 b is depicted in agenerally open configuration, such that first jaw mechanism 112 b doesnot contact or is situated at a distance from second jaw mechanism 114b. The treatment system includes a serpentine electrode or ablationmember 115 b disposed on second jaw mechanism 114 b. The first jawmechanism 112 b includes a corresponding electrode or ablation member(not shown) that faces toward ablation member 115 b. In some cases, atreatment system may present a disposable dedicated bipolar clamp havingflip jaws and a symmetric jaw-release on a plunger style body.

FIG. 2 shows aspects of a treatment system 200 according to embodimentsof the present invention. Treatment system 200 includes a clamp assembly210, an actuator assembly 220, and a coupling assembly 230 in operativeassociation with both the clamp assembly and the actuator assembly.Clamp assembly 210 includes a first jaw mechanism 212 and a second jawmechanism 214. First jaw mechanism 212 is disposed proximal to secondjaw mechanism 214. The jaw mechanisms may include ablation assemblies,as well as support assemblies for holding the ablation assemblies. Forexample, as shown in FIG. 2 , second jaw mechanism 214 includes anablation assembly 216 having a proximal electrode 216 a and a distalelectrode 216 b. The proximal and distal electrodes are coupled with asupport assembly 215. First jaw mechanism 212 provides a similarconfiguration, and has one or more electrodes (not shown) that facetoward electrodes 216 a, 216 b of distal jaw mechanism 214. In use, thesurgeon or operator can use the handle or actuator assembly 220 formanipulating the treatment system, opening and closing the jawmechanisms, activating ablation members such as electrodes 216 a, 216 b,and the like. Treatment system 200 can be generally configured to beintroduced through a minimally invasive sheath, trocar, or incision. Insome cases, treatment system 200 can be used in open surgicalprocedures. Coupling assembly 230 may include a shaft or other elongatemember 233. In some embodiments, the shaft or elongate member may bemalleable. Optionally, elongate member 233 may articulate about at leastone joint and/or may be steerable for positioning the system 200.Elongate member may be made of any suitable material, such as metal,ceramic, polymers, or any combination thereof, and may be rigid alongits entire length or rigid in one or more parts and flexible in one ormore parts. In some embodiments, ablation assembly 216, support assembly215, or both, are coupled with or otherwise in operative associationwith actuator assembly 220, optionally via coupling assembly 230.According to some embodiments, the jaw or tubular shaft elements mayinclude a high strength material such as metal, carbon fiber, or thelike.

Clamp assembly 210 may be disposed on or near a distal end 234 ofcoupling assembly 230, and can be generally configured to open and closeto grasp epicardial or other tissue between the opposing jaw mechanisms212, 214. As shown here, actuator assembly 220 is coupled with couplingassembly 230 via a proximal portion 232 of the coupling assembly. Anablation assembly 216 may use any suitable energy source for ablatingtissue. In some embodiments, multiple ablation members may be used in abipolar treatment technique. For example, one electrode (e.g. electrode216 a) of a bipolar ablation member may be coupled with one opposing jaw(e.g. distal jaw 214) and another corresponding electrode (not shown)may be coupled with the other opposing jaw (e.g. proximal jaw 212).

Aspects of clamp assembly 210, such as jaw mechanisms 212, 214 orablation assemblies 216, may be shaped to contact and ablate theepicardial tissue in a pattern such as, but not limited to, a U-shapedpattern, an L-shaped pattern, a circular pattern, a nonlinear pattern,or a linear pattern. Actuator assembly 220 may enable the physician toperform one or more various system operations, such as opening andclosing the jaw mechanisms 212, 214, activating an ablation assembly216, changing an angle of orientation of a jaw mechanism 212, 214,straightening or bending a jaw mechanism 212, 214, or the like. Forexample, an actuator assembly may include a trigger-like actuator.Optionally, an actuator assembly may include a turnable dial.

Generally, a jaw mechanism 212, 214 may have any suitable configurationfor contacting a surface of a heart, for grasping epicardial or othertissue to be ablated, for placing ablation members 216 a, 216 b incontact with tissue to be ablated, or for any combination thereof. Assuch, jaw mechanisms 212, 214 may be straight, curved, bent, orotherwise configured for contacting, grasping, or ablating tissue, orany combination thereof. In some embodiments, jaw mechanisms 212, 214may be adjustable via actuator assembly 220, so as to allow their shapesto be bent, straightened, or the like, during a procedure. In somecases, jaw mechanisms 212, 214, can be retractable. For example, jawmechanisms 212, 214 may be retracted within coupling assembly 230 uponone or more occasions during an operation. Retraction may help protect apatient as well as a jaw mechanism during insertion and advancement ofthe system within the patient.

In some embodiments, the treatment system may further include aninsulation member at least partially surrounding or covering one or morethe actuator assembly, coupling assembly, or clamp assembly. Such aninsulation member can operate to protect body structures in the vicinityof the epicardial tissue from being ablated or damaged due to heat orelectrical current. In some cases, ablation members such as electrodes216 a, 216 b may be adjustable to deliver two or more varying amounts ofablative energy to two or more locations on the epicardial tissue.Various embodiments may further include at least one sensor for sensinga quantity of ablation provided by the ablation member to the tissue.

FIG. 3 shows aspects of a treatment system 300 according to embodimentsof the present invention. Treatment system 300 includes a clamp assembly310, an actuator assembly 320, and a coupling assembly 330 in operativeassociation with both the clamp assembly and the actuator assembly.Clamp assembly 310 includes a first jaw mechanism 312 and a second jawmechanism 314. First jaw mechanism 312 is disposed proximal to secondjaw mechanism 314. The jaw mechanisms may include ablation assemblies,as well as support assemblies for holding the ablation assemblies. Forexample, as shown in FIG. 3 , second jaw mechanism 314 includes anablation assembly 316 having a proximal electrode 316 a and a distalelectrode 316 b. The proximal and distal electrodes are coupled with asupport assembly 315. First jaw mechanism 312 provides a similarconfiguration, and includes an ablation assembly 317 and a supportassembly 319. The ablation assembly 317 includes a proximal electrode317 a and a distal electrode 317 b that face toward electrodes 316 a,316 b, respectively, of distal jaw mechanism 314. In use, the surgeon oroperator can use the handle or actuator assembly 320 for manipulatingthe treatment system, opening and closing the jaw mechanisms, activatingablation members such as electrodes 316 a, 316 b, 317 a, 317 b, and thelike. Treatment system 300 can be generally configured to be introducedthrough a minimally invasive sheath, trocar, or incision. In some cases,treatment system 300 can be used in open surgical procedures. Couplingassembly 330 may include a shaft or other elongate member 333. In someembodiments, the shaft or elongate member may be malleable. Optionally,elongate member 333 may articulate about at least one joint and/or maybe steerable for positioning the system 300. Elongate member may be madeof any suitable material, such as metal, ceramic, polymers, or anycombination thereof, and may be rigid along its entire length or rigidin one or more parts and flexible in one or more parts. In someembodiments, ablation assemblies 316, 317, support assemblies 315, 319,or any combination thereof, are coupled with or otherwise in operativeassociation with actuator assembly 320, optionally via coupling assembly330.

Clamp assembly 310 may be disposed on or near a distal end 334 ofcoupling assembly 330, and can be generally configured to open and closeto grasp epicardial or other tissue between the opposing jaw mechanism312, 314. An ablation assembly 316 may use any suitable energy sourcefor ablating tissue. In some embodiments, multiple ablation members maybe used in a bipolar treatment technique. For example, one electrode(e.g electrode 316 a) of a bipolar ablation member may be coupled withone opposing jaw (e.g. distal jaw 314) and another correspondingelectrode (e.g. electrode 317 a) may be coupled with the other opposingjaw (e.g. proximal jaw 312). Optionally, ablation assemblies may includeone unipolar ablation device or any of the ablation devices describedelsewhere herein.

Aspects of clamp assembly 310, such as jaw mechanisms 312, 314 orablation assemblies 316, 317 may be shaped to contact and ablate theepicardial tissue in a pattern such as, but not limited to, a U-shapedpattern, an L-shaped pattern, a circular pattern, or a linear pattern.Actuator assembly 320 may enable the physician to perform one or morevarious system operations, such as opening and closing the jawmechanisms 312, 314, activating an ablation assembly 316, 317, changingan angle of orientation of a jaw mechanism 312, 314, straightening orbending a jaw mechanism 312, 314, or the like. For example, an actuatorassembly may include a trigger-like actuator. Optionally, an actuatorassembly may include a turnable dial.

Generally, a jaw mechanism 312, 314 may have any suitable configurationfor contacting a surface of a heart, for grasping epicardial or othertissue to be ablated, for placing ablation members 316 a, 316 b, 317 a,317 b in contact with tissue to be ablated, or for any combinationthereof. As such, jaw mechanisms 312, 314 may be straight, curved, bent,or otherwise configured for contacting, grasping, or ablating tissue, orany combination thereof. In some embodiments, jaw mechanisms 312, 314may be adjustable via actuator assembly 320, so as to allow their shapesto be bent, straightened, or the like, during a procedure. In somecases, jaw mechanisms 312, 314, can be retractable. For example, jawmechanisms 312, 314 may be retracted within coupling assembly 330 uponone or more occasions during an operation. Retraction may help protect apatient as well as a jaw mechanism during insertion and advancement ofthe system within the patient. Ablation members such as electrodes 316a, 316 b, 317 a, 317 b, may be bipolar RF members, unipolar RF members,or any other suitable ablation devices.

In some cases, the tissue treatment systems can have a spring loadedmechanism that allows an indirect connection between the handle and theclamp members or jaws. Hence, during the initial stage of the clampingprocess, there can be a 1:1 ratio between movement of the handle andmovement of the clamp members or jaws. However, during the later stageof the clamping process when the clamp members or jaws are sufficientlyclose to one another, optionally applying sufficient pressure on theatrium, there may not be a 1:1 ratio between movement of the handle andmovement of the clamp members or jaws. Rather, a handle movement resultsin a smaller corresponding movement of the clamp members and jaws. Thetreatment assemblies can be configured as inserts that are removablewith respect to the clamp members or jaws. According to someembodiments, the treatment assemblies may be disposable, replaceable, orboth, and the clamp or support member can be sterilizable, reusable, orboth.

According to some embodiments, a treatment system can be convertible;that is, the system can convert from a bipolar configuration tomonopolar configuration and back to a bipolar configuration according tothe surgeon's need or decision. In some cases, a monopolar device doesnot include jaws and can be in the form of a malleable electrode thatpresents a contact strip or surface to deliver RF energy to tissue fromany direction and from any shape it is bent into. In some cases, amonopolar probe resides within or is a part of the handle or shaftstructure of a bipolar clamp. The monopolar electrode can reside in onejaw and act as the active electrode when in a bipolar configuration, andthe other jaw can act as the indifferent (ground) electrode. When thesurgeon converts the device to a monopolar configuration, for example bypulling the monopolar probe assembly out of the rest of the device, theprobe acts as a monopolar device because the return path for energy isnow through the ground pad on the patient. When the surgeon is done withthe monopolar RF application, he or she may choose to straighten theelectrode and reinsert it into the bipolar handle to make that partfunctional again.

In some embodiments, the treatment system may further include aninsulation member at least partially surrounding or covering one or morethe actuator assembly, coupling assembly, or clamp assembly. Such aninsulation member can operate to protect body structures in the vicinityof the epicardial tissue from being ablated or damaged due to heat orelectrical current. In some cases, ablation members such as electrodes316 a, 316 b, 317 a, 317 b may be adjustable to deliver two or morevarying amounts of ablative energy to two or more locations on theepicardial tissue. Various embodiments may further include at least onesensor for sensing a quantity of ablation provided by the ablationmember to the tissue.

Actuator assembly 320 may include a symmetric, unified release trigger.In some cases, the actuator assembly may have a plurality of separatedratchet teeth. In use, the operator or surgeon may close or clamp thejaw mechanisms together by activating a handle or plunger of theactuator assembly. Relatedly, the operator may release the jawmechanisms from a clamped configuration by activating a release triggerof the actuator assembly. In some cases, a release trigger may include abutton or a slide mechanism. The treatment system may be spring loaded,such that release of a ratchet mechanism allows release of the jawmechanisms and the spring allows an automatic position return of theratchet mechanism.

Embodiments of the present invention encompass a variety of mechanismswhich may be used to open or close the jaw mechanisms. In some cases,treatment systems may include a pliers assembly configured to open orclose the jaw mechanisms. In some cases, treatment systems may include ascissors assembly configured to open or close the jaw mechanisms.Optionally, a pliers or scissors assembly can include two members havinga central pivot, whereby the closing of the handle portion closes thedistal portions by changing the angle between the two members fromsomething greater than zero to something less than the starting number,generally bringing together the distal ends. In some cases, treatmentsystems may include a sliding mechanism or assembly configured to openor close the jaw mechanisms. Optionally, the treatment system mayinclude a plunger assembly configured to open or close the jawmechanisms. Exemplary actuator assemblies may include pistol grips,hinged grips, and the like. In some cases, an actuator assembly mayprovide for direct activation or coupling of the jaw mechanisms, suchthat when the surgeon moves a portion of the actuator assembly by agiven amount, the actuator assembly causes the jaw mechanism to move thesame amount in a 1:1 ratio. In some cases, an actuator assembly mayprovide for indirect activation or coupling of the jaw mechanisms, suchthat when the surgeon moves a portion of the actuator by a given amount,the actuator assembly causes the jaw mechanism to move in differingamount. An actuator assembly may be configured to limit, attenuate, oramplify the amount of clamping force applied to a tissue based on theamount of squeezing or activating force manually applied by a surgeon.

In some instances, the treatment system can include a jaw releasetrigger that is symmetric about two planes, and that allows or actuatesrelease of the jaw mechanisms such that the jaw mechanisms translaterelative to each other in an upward or downward manner. Such actuationcan be performed without changing the jaw release finger motion. In somecases, a jaw mechanism release or opening action can be accomplishedwithout changing the operator's basic hand position on the handle. Thesystem can be configured so that the operator can reach or use therelease trigger located in an ergonomically efficient position. Arelease trigger may be self-centering and momentary. In some cases, arelease trigger can have a single re-centering spring that is captive inthe body shell and actuated at either end by a finger that reaches intothe entrapping space from the moving trigger portion from either end tocompress the spring as the trigger is pushed off-center.

FIG. 4 shows a treatment system 400 in a position for performing anablation or treatment procedure on epicardial tissue of heart 440.Treatment system 400 includes a clamp assembly 410 having first andsecond jaw mechanisms 412, 414, and can be configured to ablate in apattern approximating two lines adjacent the right pulmonary veins 442,444. As discussed elsewhere herein, jaw mechanisms 412, 414 can berotated as desired to provide a variety of ablation configurations.Additionally, treatment system 400 may be moved to a variety ofpositions to ablate multiple patterns in multiple locations on theepicardial tissue.

Treatment system 400 includes a handle or actuator assembly 420 disposedtoward a proximal portion of the system. As shown here, first and secondjaw mechanisms 412, 414, which may include two bipolar ablation clamps,are disposed toward a distal portion of the system. The jaw mechanisms412, 414 can be curved or shaped. In some cases, jaw mechanisms 412, 414are curved and adjustably rotatable, so that for each jaw mechanism 412,414, a concave portion or arc of the jaw mechanism can face toward thehandle, away from the handle, toward the right side of the handle,toward the left side of the handle, or toward any desired directionrelative to the handle. In some cases, a jaw mechanism can be inconnectivity with a treatment assembly or ESU. During use, the tissuetreatment system can be used to contact the cardiac tissue, which can beeffectively accomplished for example by the curvature orientation. Thecurved or contoured shape of the jaw mechanisms can allow the treatmentsystem to be placed on the heart without impinging upon the pulmonaryveins. Hence, there is an increased likelihood of ablating tissue of theatrium, as opposed to ablating tissue of the pulmonary veins themselves.Treatment system 400 is well suited for use in surgical methods whereaccess ports are not employed. For example, the treatment system can beinserted into a patient via a 3-4 inch thoracotomy. In use, the jawmechanisms are placed at or near the ostia, and actuated until theopposing jaw members are approximately 2-5 millimeters apart. Thisaction serves to collapse the atrium near the pulmonary veins. Anablation is performed, and the clamping pressure is released thusallowing the atrium to return to the uncompressed state.

Electrosurgical Unit Operation

According to some embodiments, a treatment system may include or becoupled in operative association with an electrosurgical unit (ESU) thatcan supply and control power to an ablation assembly of the treatmentsystem. FIGS. 5, 6A, and 6B illustrate aspects of an ESU 600 thatsupplies and controls power, such RF power, to a treatment system duringa treatment procedure. As shown here, ESU 600 includes a controller 635,a source of RF power 637 that is controlled by the controller, and aplurality of displays and buttons that are used to set the level ofpower supplied to one or more electrodes at various locations on anelectrode. The exemplary ESU 600 illustrated is operable in a bipolarmode, where tissue coagulation energy emitted by an electrode 502 isreturned through a return electrode 502 a, and a unipolar mode, wherethe tissue coagulation energy emitted by the electrode is returnedthrough one or more indifferent electrodes (not shown) that areexternally attached to the skin of the patient with a patch or one ormore electrodes (not shown) that are positioned in the blood pool. Thereturn electrode 502 a, which in a bipolar configuration can beidentical to the electrode 502, may be connected to the ESU 600 by apair of power return lines 504 a and 506 a. The return electrode 502 aand power return lines 504 a and 506 a together define a returnelectrode assembly 500 a.

In some embodiments, return electrode 502 a can be an indifferentelectrode. In a bipolar configuration, an active electrode and anindifferent electrode can cooperate to help form a complete circuit ofRF energy, for example when the two electrodes are placed across ananatomical feature such as the atria or other patient tissue. Energy cantravel from the active electrode through the tissue to the indifferentelectrode. An active electrode can be coupled with one or more RF wires.An indifferent electrode can provide a return path, optionally as asingle wire, operating as a ground. In use, energy passing through theelectrodes can raise the temperature of the intervening tissue, forexample tissue which is secured between two clamp mechanisms. In turn,the heated tissue can raise the temperature of the electrodes. In somecases, active electrodes, indifferent electrodes, or both, can be cooledwith internal cooling mechanisms. In exemplary embodiments, energyapplied by the electrodes operates to kill tissue without a significantconcomitant rise in tissue temperature. In some instances, a treatmentsystem may include multiple active electrodes along a length of a clamp.Each active electrode can be coupled with an RF wire that suppliedenergy to the electrode.

ESU 600 can be provided with a power output connector 636 and a pair ofreturn connectors 638. The electrode 502 is connected to the poweroutput connector 636 by way of the power supply lines 504 and 506 and apower connector 540, while the return electrode 502 a is connected toone of the return connectors 638 by way of the power return lines 504 aand 506 a and a return connector 542. In some cases, the ESU output andreturn connectors 636 and 638 have different shapes to avoid confusionand the power and return connectors 540 and 542 are correspondinglyshaped. For example, power connector 540 may have a circular shapecorresponding to an ESU power output connector 636 having a circularshape, and return connector 542 may have a rectangular shapecorresponding to an ESU return connector 638 having a rectangular shape.

ESU 600 can be configured to individually power and control a pluralityof electrodes. In some cases, the electrodes may be about 10 mm inlength. Optionally, a bipolar clamp configuration may include two 32 mmactive electrodes and one 70 mm electrode. Such individually powered orcontrolled configurations may be referred to as providing “multi-channelcontrol.” In some cases, ESU 600 can include up to 8 channels, or more.ESU 600 can also be configured to individually power and control two ormore portions of a single electrode as well as two or more portions ofeach of a plurality of electrodes during a lesion formation procedure.Electrode 502 as shown here can be divided into two portions for powercontrol purposes. The electrode portion connected to the power supplyline 504 on one side of the dash line in FIG. 6A (e.g. the left side)and the electrode portion connected to the power supply line 506 on theother side (e.g. the right side) of the dash line. According to someembodiments, the dash line does not represent a physical division andthe electrode 502 is a continuous, unitary structure. Electrode 502 canbe placed adjacent to tissue and power to one portion can be controlledby control channel CH1 and power to the other portion is controlled bycontrol channel CH2. The power can be, although not necessarily,supplied to both portions simultaneously.

According to some embodiments, the level of power supplied to theelectrode 502 by way of the power supply line 504 may be controlled bythe ESU. In one exemplary control scheme, the level of power supplied tothe electrode 502 by way of the power supply line 506 can be controlledby the ESU.

The amount of power required to coagulate tissue typically ranges from 5to 150 w. Aspects of suitable temperature sensors and power controlschemes that are based on sensed temperatures are disclosed in U.S. Pat.Nos. 5,456,682, 5,582,609 and 5,755,715, the contents of which areincorporated herein by reference.

According to some embodiments, a plurality of spaced electrodes can beprovided that operate in a unipolar mode. Each of the electrodes can beconnected to a respective pair of power supply lines. Each of theelectrodes on a surgical probe can be divided into portions for powercontrol purposes, and the level of power supplied to some electrodeportions by way of power supply lines can be controlled by the ESU,while the level of power supplied to other electrode portions by way ofpower supply lines can be controlled by the ESU.

As noted elsewhere herein, in some cases an ESU can be configured toapply voltage pulses of 500-1000 volts between the jaw faces using pulsedurations of 0.02-0.1 msec, which in most instances is sufficient tokill all or substantially all myocardial cells between the jaw faces.When it is desired that all or substantially all of the myocardial cellsbe irreversibly damaged by the high voltage gradients within thetargeted tissue, an ESU can be configured to deliver 10-50 pulses over a1 to 60 second time interval.

Monopolar Ablation Technologies I

For exemplary ablation technologies, including monopolar techniques,that use long linear electrodes, some embodiments use standard returnpads on the skin. In such configurations, voltage pulses of 1000-2000volts applied between the linear electrodes and the return pad withpulse durations of 0.02-0.1 msec can be sufficient to kill all orsubstantially all myocardial cells within about 5 mm of the electrodes.When it is desired that all or substantially all of the myocardial cellsbe irreversibly damaged by the high voltage gradients within thetargeted tissue, 5-50 pulses can be delivered over a 1 to 60 second timeinterval. For such electrode configurations and voltage deliverymethods, the region of tissue subjected to lethal voltage fields can bedetermined by the amplitude of the applied pulses and the pulse width.For a 0.05 msec pulse width, multiple 1000 volt pulses are typicallysufficient to ablate tissue to a depth of about 5 mm. To achievereliable lesions depths of about 10 mm, it may be helpful to increasethe voltage amplitude to about 2000 volts. In tissue regions that arethick, for example about 10 mm, lesions typically will be also be wide,the lesion having approximately a semicircular cross section. In thinnertissue regions, the lesion width typically will be thinner, being abouttwice as wide as the tissue is thick. In other words, the lesion will beabout 8 mm wide where the atrial wall is about 4 mm thick. Often, therewill be little or no cellular damage near the return pads, because withthe large surface areas of the pads, the current densities are low atthe skin level and therefore voltage gradients are low, generally lowerthan about 10V/cm.

Referring now to the drawings, FIG. 7 illustrates aspects of a tissuetreatment system according to embodiments of the present invention.Tissue treatment system 700 is well suited for use in medical proceduresthat involve ablating cardiac tissue of a human heart, such as thosetechniques disclosed in U.S. Patent Application Nos. 60/939,201 filed:May 21, 2007, and 61/015,472 filed Dec. 20, 2007. The content of each ofthese applications is incorporated herein by reference. Tissue treatmentsystem 700 includes a tissue contacting assembly 710, optionally havinga suction pod 712. Tissue treatment system 700 also includes a treatmentassembly 720 that extends through a length of the tissue contactingassembly. In some cases, tissue treatment system 700 also includes oneor more holders 730 that can hold treatment assembly 720 within orrelative to tissue contacting assembly 710. Typically, during a surgicalprocedure the treatment assembly is coupled with an energy source. Whena treatment or medical procedure is completed, the treatment assemblymay be decoupled from the energy source.

According to some embodiments, a treatment method may include ablatingand monitoring a cardiac tissue of a patient with tissue treatmentsystem 700. Treatment methods may also include techniques for placingtissue treatment system 700 at a desired location within a patient. Forexample, a treatment method may include positioning tissue treatmentsystem 700 at or near the pulmonary veins of a patient. A surgeon oroperator may use an obturator and introducer assembly to posit thetissue treatment system at or near a specific location or anatomicalfeature of the patient. Treatment assembly 720 can include any of avariety of tissue ablation mechanisms. In some cases, a treatmentassembly 720 can include an ablation element that transmits or deliversRF energy to patient tissue. Optionally, suitable ablation elements cantransmit or deliver infrared laser energy, high intensity focusedultrasound (HIFU) energy, microwave energy, cryoablation energy, and thelike. Embodiments encompass treatment assemblies having multipleablation elements, such as RF electrodes. In some cases, a treatmentassembly may include a single ablation element, such as a single RFablation electrode. Typically, an RF electrode is activated in itsentirety during an ablation procedure. Longer lesion lengths can be madeby moving the electrode and ablating so that the ablations from the twoablation applications overlap. The procedure can be repeated until thedesired lesion pattern is completed.

FIG. 8 depicts an obturator and introducer assembly 800 according toembodiments of the present invention. Obturator and introducer assembly800 includes an obturator 810 and an introducer 850. The introducerincludes a tube 852 that is pre-bent or pre-formed into a particularshape, for example a curved or J shape. The obturator includes a handle812 and a shaft 814. As shown here, obturator shaft 814 can be insertedinto introducer tube 852, so that shaft 814 extends substantiallythrough a length of tube 852. The introducer can be fabricated with arelatively flexible material, and the obturator can be fabricated with arelatively rigid material, so that when the obturator is inserted intothe introducer, the introducer conforms to or toward the shape of theobturator. When obturator shaft 814 is removed from introducer tube 852,the tube can return to its preformed or pre-bent shape. A distal end 854of introducer 850 can have a designated region for grasping. During amedical procedure, a grasping instrument may be introduced through thesame or a second incision to grasp the distal end or portion 854 of theintroducer 850. An operator or surgeon can use the grasping instrumentto pull distal end or portion 854 of the introducer outside the body ofthe patient. A distal end or portion 740 of the tissue treatment systemshown in FIG. 7 can be attached with a proximal end or portion 856 ofthe introducer. Thus, the introducer can be withdrawn or otherwisemaneuvered until the tissue treatment system is positioned at or near adesired location within the patient.

According to some embodiments, a treatment method may include insertingan obturator into an introducer, and advancing the combined obturatorand introducer assembly through a first incision into the transversesinus cavity. When the combined assembly has been positioned in adesired area or location at or near the pulmonary veins, the obturatorcan be withdrawn from the introducer, and the introducer can be allowedto assume a pre-formed shape which may at least partially reach aroundthe pulmonary veins, possibly also guided by contact with thepericardium. In some cases, the introducer is long enough to be insertedfrom thoracotomy into transverse sinus cavity around the pulmonary veinsand out through the oblique sinus and out through the same or adifferent thoracotomy. Another instrument can be advanced through thesame or different thoracotomy to grasp the distal end of the introducer.The introducer can be pulled around the pulmonary veins until the distalend is outside the body of the patient. At this point, both the proximaland distal ends of the introducer can be disposed outside the body ofthe patient.

A proximal end of introducer can be attached, for example with a luerfitting, to the distal end of a tissue treatment system. The introducer,the tissue treatment system, or both, may include indication markers andlines which an operator can use or rely upon when positioning the tissuetreatment system, so as to ensure the desired or proper placement. Forexample, circumferential indication markers on the introducer can beused as depth measurements, and an indication stripe on the surface ofthe introducer can be aligned with similar markings on the tissuetreatment system to ensure that the ablation device will be facingproperly when inserted. In some embodiments, the introducer can havetorsional rigidity to facilitate steerability. Further, the introducercan include a material having a highly visible color for endoscopicvisualization and distinguishing from natural anatomical colors.

Once the tissue treatment system is in position, suction can be appliedto adhere the ablation device to the tissue surrounding the pulmonaryveins. The tissue treatment system can be placed into position via anyof a variety of suitable techniques, such as those described in U.S.Patent Application Nos. 60/939,201 and 61/015,472 filed May 21, 2007 andDec. 20, 2007, respectively. The content of each filing is incorporatedherein by reference. Ablation energy can be applied. Once treatment iscomplete, the tissue treatment system can be removed.

According to some embodiments, treatment methods may include performinga medical procedure that entails creating a continuous lesion encirclingor partially encircling the pulmonary veins to electrically isolate thepulmonary veins. Treatment methods may also include creating ablationlesions in the left and/or right atrium, vena cava, endocardium to themitral valve annulus, or along the left atrial appendage to create aMaze-like lesion set for treatment of atrial fibrillation.

FIG. 9 illustrates aspects of a treatment assembly 900 according toembodiments of the present invention. Such systems can include one ormore stimulation electrode for pacing or stimulating tissue. Stimulationelectrodes may be used to perform a variety of functions before, during,and after a lesion formation procedure. For example, stimulationelectrodes may be used to confirm tissue contact prior to supplyingcoagulation energy, to evaluate the lesion as the coagulation energy issupplied, and to confirm whether or not a therapeutic lesion has beenformed after the coagulation energy has been discontinued. Stimulationenergy may be used because non-viable tissue, for example coagulatedtissue, is difficult or impossible to stimulate and typically will notpropagate stimulation energy to nearby tissue.

Hence, treatment assembly 900 as depicted in FIG. 9 includes one or morepacing or stimulation electrodes 910 that are capable of providingpulses of energy that stimulate, but do not coagulate, tissue. Powerdelivered to tissue for stimulation purposes will typically besignificantly less than that which would form a transmural or otherwisetherapeutic lesion in tissue. An exemplary stimulation energy deliverycan include two stimulation pulses per second, each pulse being 1millisecond. In some embodiments, the amplitude can be 10 mA, whichwould create 5 V, for a total power delivery of 100 μW. In contrast, theamount of power used for coagulating tissue can often range from about 5to about 150 W. The amplitude may be increased in some instances, forexample where the stimulation pulses are being supplied at the same timeas the tissue coagulation energy. Treatment assembly 900 also includesone or more ablation or coagulation electrodes 920. The stimulationelectrodes can be disposed on energy transmission surfaces of a variablespacing structure 930. Alternatively, the stimulation electrodes may belocated between a resilient member 932 and a barrier member 934 or, ininstances where there is no barrier member, simply on the exterior ofresilient member 932. The stimulation electrodes may also be used inconjunction with a resilient member that includes conductive fibers. Apacing or stimulation electrode 910 may be connected with a signal wire912. Optionally, a signal wire can be configured such that it will notchange the mechanical properties of the resilient material. Suitablesignal wires can include wires that are 38 gauge or smaller.

As shown here, signal wire 912 traverses resilient material 932 and canenter a support structure near stimulation electrode 910. For example, aportion of signal wire 912 can be disposed between the windings of anunderlying coagulation electrode 920, between two adjacent underlyingcoagulation electrodes 920, or just proximal to an underlyingcoagulation electrode 920. A signal line or wire 912 can be configuredto provide connectivity between pacing or stimulation electrode 910 andan EP recording apparatus or ESU. One or more stimulation electrodes canbe positioned such that they are located between, and aligned with, oneor more coagulation electrodes. In some cases, a stimulation electrodecan be aligned with a channel, such as a linear channel.

The placement of tissue stimulation electrodes on the same surgicaldevice as the tissue coagulation electrodes allows the physician toquickly and easily confirm tissue contact and evaluate the lesion withlittle or no movement of the device. Stimulation electrodes can belocated between the energy transmitting portions of treatment assembly900 and can also be located in a current path between treatment assembly900 and the tissue. This arrangement can provide accurate informationwhen the stimulation electrodes are used to confirm tissue contact priorto supplying coagulation energy, because the stimulation electrodes arein contact with the portions of the tissue structure through whichcurrent will be transmitted, as opposed to being in contact with tissuethat may be further from the current path.

The location of the stimulation electrodes can also provide accurateinformation concerning the lesion itself during and after the tissuecoagulation procedure because the stimulation electrodes are in directcontact with the coagulated tissue. The assessment of the lesion can belocalized. For example, the assessment can be made directly on thetarget tissue within the current path. Therefore, a lesion assessmentprocess can be easier to implement than those which involve stimulatingtissue on one side of a lesion and sensing tissue on the other. Here,the assessment can involve a determination whether or not stimulation ofthe tissue adjacent to the lesion occurs, as opposed to an assessment ofthe propagation delay between the stimulation pulse on one side of thelesion and the stimulation on the other.

With respect to methods by which tissue contact may be confirmed afterthe physician has positioned treatment assembly 900 on a tissuestructure, the stimulation electrodes may be used to supply pulses ofstimulation energy, sometimes referred to as pacing pulses, to thetissue in the current path CP between treatment assembly 900 and thetissue. The stimulation energy can be supplied through one or moresingle stimulation electrodes. The physician can monitor the adjacenttissue, either visually or with a monitor such as an ECG to determinewhether that tissue was stimulated. In the context of the treatment ofatrial fibrillation, for example, the procedure may be performed aftertreatment assembly 900 is epicardially positioned about one or more ofthe pulmonary veins. If the stimulation energy stimulates, or paces, theadjacent tissue, for example the left atrium, the physician can knowthat proper contact has been achieved for the associated portions oftreatment assembly 900. This process may be sequentially repeated withany desired combination of stimulation electrodes to insure or evaluatetissue contact with the other portions of treatment assembly 900.Thereafter, and without moving treatment assembly 900, tissuecoagulation energy may be applied to the tissue in the current path withone or more coagulation electrodes to form a lesion.

Stimulation energy can be used while the tissue coagulation energy isbeing supplied in order to determine when a transmural lesion has beencompletely formed. Here, stimulation energy pulses may be supplied bystimulation electrodes to the tissue in the current path. The tissueadjacent to the current path can be monitored, either visually or withan ECG, to determine when the adjacent tissue is no longer beingstimulated. The supply of tissue coagulation energy may be discontinuedin response to such a determination. For example, if a tissue treatmentsystem is programmed to supply coagulation energy for 30 seconds, thesupply of energy could end after 25 seconds if the lesion is completedearlier than was anticipated, as determined by the inability tostimulate the adjacent tissue. This may be accomplished either manuallyor automatically.

Tissue may become non-stimulatable before it is irreversibly coagulatedor otherwise irreversibly damaged. Accordingly, tissue coagulationenergy can continue to be supplied for a few seconds after the adjacenttissue ceases to be stimulated by stimulation energy pulses. That is,there can be a brief delay before the coagulation energy isdiscontinued. It should also be noted that while coagulation energy isbeing supplied by the coagulation electrodes, the stimulation energy canbe supplied at a significantly higher amplitude, for example 5 timeshigher, than it would be before or after the coagulation procedurebecause tissue that is heated can be harder to stimulate. For example,if 4 mA pulses are suitable before and after the coagulation procedure,then 20 mA pulses can be used during the coagulation procedure.

Stimulation energy may be supplied after tissue coagulation energy hasbeen discontinued, either at the end of the pre-programmed period orbased on the sensed completion of the lesion, in order to determinewhether a transmural lesion has been formed. Without moving treatmentassembly 900, stimulation energy pulses may be supplied by stimulationelectrodes to the tissue in the current path. The adjacent tissue can bemonitored, either visually or with the ECG, to determine whether theadjacent tissue can be stimulated. If not, the physician may assume thata transmural lesion has been formed. In those instances where the lesionis incomplete, one or more stimulation electrodes may be used todetermine where the gap, or the portion of the lesion that is nottransmural, is located. Additional coagulation energy may then besupplied as necessary or desired to complete the lesion. It may be thecase that the entire lesion is not transmural, which may require thecoagulation procedure to be at least partially repeated.

Pacing or stimulation electrodes 910 can be relatively small, solid, lowprofile devices. For example, a stimulation electrode can be configuredto be small enough that it does not form transmural myocardial lesions.Suitable surface are sizes can be about 0.2 mm2 to about 10 mm2, andsuitable thicknesses can be about 0.01 mm to 0.5 mm. For example, astimulation electrode can have a surface area of about 1 mm2 and athickness of about 0.1 mm. Suitable materials include platinum, platinumiridium, stainless steel, gold, silver-silver chloride or othernon-toxic metals. Stimulation electrodes may also be formed by coating aconductive material onto variable spacing structures 930 or anotherunderlying structure using conventional coating techniques or an ionbeam-assisted deposition (IBAD) process. Suitable conductive materialsinclude platinum-iridium and gold. An undercoating of nickel, silver ortitanium may be applied to improve adherence. Conductive ink compounds,such as silver-based flexible adhesive conductive ink (polyurethanebinder) or metal-based adhesive conductive inks (e.g. platinum, gold, orcopper based) may also be pad printed in place. With respect toassembly, signal wire 912 may be welded or soldered to solid pacing orstimulation electrode 910 prior to assembly, while coated/printedelectrodes may be formed onto the ends of signal wires that are alreadyin place.

Exemplary tissue treatment systems and methods can involve providingmonopolar stimulation pulses from stimulation electrodes 910. Forexample, a monopolar stimulation pulse can be generated by a pair ofstimulation electrodes 910 which may be associated with one or morecoagulation electrodes 920 that form the lesion. Stimulation electrodepairs may be used to supply pulses of stimulation energy to the tissuein the current path CP associated with one of the coagulationelectrodes. The physician can monitor the adjacent tissue in the tissuestructure, either visually or with an ECG, to determine whether thattissue was stimulated. This process may be sequentially repeated withthe other stimulation electrode pairs in order to insure proper tissuecontact with the applicable portions of the treatment assembly 900.Thereafter, and without moving treatment assembly 900, tissuecoagulation energy may be applied to the tissue in the current path CPwith the coagulation electrodes to form a lesion. Stimulation electrodes910 may also be used to determine lesion depth and, correspondingly,whether or not a lesion is transmural at various points along the lengthof the lesion. Stimulation energy may be used to determine lesion depthbecause non-viable tissue, for example coagulated tissue, may not bestimulatable and may not propagate stimulation energy to nearby tissue.As such, when the application of stimulation energy that shouldstimulate tissue at a known depth fails to do so, and that depth isgreater than or equal to the thickness of the body structure, it may beinferred that a transmural lesion has been formed. In some cases, thestimulation electrodes can be used on a coagulationelectrode-by-coagulation electrode basis both during and before thecoagulation process in the manner described above.

In the context of lesions formed within the heart, for example,localized current densities of at least about 2 mA/cm2 may be needed tostimulate heart tissue. With respect to current transmitted from anelectrode to tissue, the current density can be about I/2nr2, where r isthe distance from the electrode. Thus, a 1 mA stimulation pulse willtypically stimulate viable tissue that is up to about 2.8 mm from theelectrode, a 2 mA stimulation pulse will typically stimulate viabletissue that is up to about 4.0 mm from the electrode, a 10 mAstimulation pulse will typically stimulate viable tissue that is up toabout 9.0 mm from the electrode, and a 20 mA stimulation pulse willtypically stimulate viable tissue that is up to about 13.0 mm from theelectrode. The left atrium is, for example, about 3 mm thick andaccordingly, failure to stimulate with a 2 mA stimulation pulseindicates that a transmural lesion has been formed in the vicinity ofthe stimulation electrode. As noted above, these values can besubstantially increased, for example by a factor of five, when thestimulation pulses are being supplied at the same time as thecoagulation energy.

As shown in FIG. 9 , pacing or stimulation electrodes 910 can bepositioned between the coagulation electrodes 920 and target tissue. Assuch, the stimulation electrodes 910 can be in the current path of eachcoagulation electrode 920. Optionally, stimulation electrodes can bedisposed between the current paths associated with coagulationelectrodes 920. As described elsewhere herein, treatment assembly 900can be used in conjunction with a standard return pad placed on thepatient's skin. Voltage pulses of 1000-2000 volts, for example generatedby an ESU in operative association with treatment assembly 900, can beapplied between the linear electrodes and the return pad with pulsedurations of 0.02-0.1 msec. Such treatment protocols can be sufficientto kill all or substantially all myocardial cells within about 5 mm ofthe electrodes. When it is desired that all or substantially all of themyocardial cells be irreversibly damaged by the high voltage gradientswithin the targeted tissue, 10-50 pulses can be delivered over a 1 to 60second time interval. For such electrode configurations and voltagedelivery methods, the region of tissue subjected to lethal voltagefields can be determined by the amplitude of the applied pulses and thepulse width. For a 0.05 msec pulse width, multiple 1000 volt pulses aretypically sufficient to ablate tissue to a depth of about 5 mm. Toachieve reliable lesions depths of about 10 mm, it may be useful toincrease the voltage amplitude to about 2000 volts.

FIGS. 10 and 11 illustrate aspects of a treatment assembly 1000according to embodiments of the present invention. In addition toforming lesions, treatment assembly 1000 may also be used to determinewhether or not therapeutic lesions have been properly formed by, forexample, supplying tissue stimulation energy on one side of a lesion.The tissue on the other side of the lesion may then be monitored todetermine whether an excitation block, typically the result of acontinuous transmural lesion, has been formed in the target tissue.Tissue stimulation energy may also be used to determine lesion depth,which in turn, allows the physician to determine whether or not a lesionis transmural. In the exemplary implementations, the tissue stimulationenergy is provided by treatment assembly 1000 that is capable ofproviding a pulse of energy that stimulates, but does not coagulate,tissue. An exemplary treatment assembly 1000 may be coupled with aconventional pacing apparatus, such as an external pulse generator. AnECG machine that is capable of monitoring and recording electricalimpulses sensed by electrodes may also be in connectivity with treatmentassembly 1000.

As described elsewhere herein, treatment assembly 1000 can be used inconjunction with a standard return pad placed on the patient's skin.Voltage pulses of 1000-2000 volts, for example generated by an ESU inoperative association with treatment assembly 1000, can be appliedbetween the linear electrodes and the return pad with pulse durations of0.02-0.1 msec. Such treatment protocols can be sufficient to kill all orsubstantially all myocardial cells within about 5 mm of the electrodes.When it is desired that all or substantially all of the myocardial cellsbe irreversibly damaged by the high voltage gradients within thetargeted tissue, 10-50 pulses can be delivered over a 1 to 60 secondtime interval. For such electrode configurations and voltage deliverymethods, the region of tissue subjected to lethal voltage fields can bedetermined by the amplitude of the applied pulses and the pulse width.For a 0.05 msec pulse width, multiple 1000 volt pulses are typicallysufficient to ablate tissue to a depth of about 5 mm. To achievereliable lesions depths of about 10 mm, it may be useful to increase thevoltage amplitude to about 2000 volts.

With respect to the stimulation energy, the power delivered to tissuefor stimulation purposes will typically be significantly less than thatwhich would form a transmural or otherwise therapeutic lesion in tissue.Stimulation electrodes may also be used for sensing. An exemplarystimulation energy delivery can include two stimulation pulses persecond, each pulse being 1 millisecond long or wide. In some cases, amaximum amplitude can be 20 mA, which can create 10 V, for a total powerdelivery of 400 μW. Another exemplary stimulation energy delivery caninclude of two stimulation pulses per second, each pulse being 1millisecond long or wide. In some cases, a maximum amplitude can be 10mA, which can create 5 V, for a total power delivery of 100 μW. Theamount of power required to coagulate tissue may in some instances rangefrom 5 to about 150 W.

Treatment assembly 1000 can be in connectivity with a pacing apparatusor an EP recording apparatus via any suitable mechanisms. In some cases,a tissue treatment system can be configured so that coagulationelectrodes will only receive coagulation energy and stimulationelectrodes will only receive stimulation energy. The functionality of atissue stimulation apparatus and EP recording apparatus may be combinedinto a single device. An EP recording apparatus may be configured todisplay measured conduction delays. Optionally, an EP recordingapparatus may be used to store expected propagation delays for varioustissue types and suction device configurations, including thepositioning of the stimulation and sensing electrodes. An EP recordingapparatus can compare the expected propagation delay (e.g. 10 ms) withno block to the measured propagation delay (e.g. 50 ms) and determinewhether or not a complete conduction block has been formed. An EPrecording apparatus can then provide an audible or visual indicationconcerning the status of the lesion. Alternatively, conduction block canbe determined by comparing a pre-treatment conduction delay, for example20 ms, to a conduction delay during or following ablation. An increasedconduction delay of more than a predetermined value for example 30 msindicates a successful ablation attempt at the site. In the aboveexample a conduction delay of 50 ms or more would indicate ablationsuccess.

Embodiments of the present invention may be used to test theeffectiveness of a lesion in any of a variety of ways. For example,after the lesion is formed, the physician may use the same surgicaldevice that was used to form the lesion, such as a tissue treatmentsystem that includes treatment assembly 1000, to perform a lesionevaluation. Stimulation electrodes that are provided on treatmentassembly 1000 may be used to stimulate tissue on one side of a lesion bypacing at a higher rate than normal, for example 120 beats/minute. Thelocal activation, if any, on the other side of the lesion can indicatewhether or not the excitation block is incomplete. The stimulationelectrodes may also be used to sense tissue within an isolated tissueregion around which a lesion has been formed. Local activation withinthe isolated region from the heart's natural stimulation is indicativeof a gap in the lesion. Additionally, the stimulation electrodes may beused to determine lesion depth. The placement of tissue stimulationelectrodes on the same surgical device as the tissue coagulationelectrodes can allow the physician to quickly and easily evaluate alesion after it has been formed.

Treatment assembly 1000 can include a suction device 1004,longitudinally extending bipolar pairs of tissue stimulation electrodes1026, and longitudinally extending bipolar pairs of sensing electrodes1028 near the lateral edges of the suction device. A plurality ofbipolar pairs of stimulation electrodes 1026 can extend along a lengthof one side of the suction device 1004, and a plurality of bipolar pairsof sensing electrodes 1028 can extend along a length of the other sideof the suction device. Each bipolar pair can be adjacent to one of thesuction ports 1010, 1014 and, accordingly, the electrodes can be heldfirmly against tissue when suction force is applied. Stimulationelectrodes 1026 can be located on one side of a slot 1020 and sensingelectrodes 1028 can be located on the other side. As such, the tissuestimulation and sensing electrodes 1026 and 1028 can be on oppositesides of treatment assembly 1000, on opposite sides of coagulationelectrodes 1110, and on opposite sides of a lesion formed by thecoagulation electrodes.

Embodiments of the present invention encompass a wide variety ofalternative stimulation and sensing electrode schemes. By way ofexample, but not limitation, the number of bipolar pairs of tissuestimulation and sensing electrodes 1026 and 1028 may range from a largenumber of pairs, as shown, to a single pair tissue stimulationelectrodes and a single pair sensing electrodes. The single pairs may belocated near the middle, measured longitudinally, of suction device1004. Another alternative is unipolar stimulation and sensing. Here,single stimulation electrodes, as opposed to a bipolar pair, may bepositioned adjacent to each of the suction ports 1010 on one side of thesuction device 1004 and single sensing electrodes may be positionedadjacent to each of the suction ports on the other side of the suctiondevice.

With respect to configuration and manufacture, the exemplary tissuestimulation and sensing electrodes 1026 and 1028 may be relativelysmall, low profile devices. For example, the electrodes may be too smallto form transmural myocardial lesions. Suitable sizes may be about 0.5mm to 1 mm in diameter, and a suitable thickness may be about 0.01 mm.Such electrodes may be formed by coating a conductive material onto thesuction device 1004 using conventional coating techniques or an IBADprocess. Suitable conductive materials include platinum-iridium andgold. An undercoating of nickel, silver or titanium may be applied toimprove adherence. Conductive ink compounds, such as silver-basedflexible adhesive conductive ink (polyurethane binder) or metal-basedadhesive conductive inks (e.g. platinum, gold, or copper based) may alsobe pad printed onto the suction device 1004. A stimulation electrode canbe connected with a signal wire or line. In some cases, a signal linesmay be very thin (e.g. about 40-50 gauge wire).

An exemplary tissue treatment system may be used to test the quality oflesions formed during a lesion formation procedure in a variety of ways.For example, a suction source may be used to maintain the position ofthe suction device 1004 after power transmission from the coagulationelectrodes 1110 has ended. A pulse of stimulation energy, for exampleabout 10 mA, may be applied to viable tissue on one side of the lesionby a pair of stimulation electrodes 1026 a. The viable tissue on theother side of the lesion may be monitored with a pair of sensingelectrodes 1028 a to detect the local excitation from the pulse ofstimulation energy. Treatment assembly 1000 can be used to measure theamount of time between the delivery of the pulse to the tissue by thestimulation electrode pair 1026 a and the detection of the localactivation by the sensing electrode pair 1028 a on the other side of thelesion. The conduction delay, or amount of time that between pulsedelivery on one side of the lesion and local activation on the other canbe indicative of the quality or extent of the lesion.

In the context of the formation of lesions within the heart, theconduction delay from the stimulation electrode pair 1026 a and thesensing electrode pair 1028 a will typically be about 10 ms when thedistance between the pairs is about 1 cm, absent a conduction block.Here, the excitation pulse may travel a relatively short distance.Conversely, when a complete conduction block is formed between thestimulation and sensing pairs, the excitation pulse may be forced totravel around the lesion. The longer travel distance can result in alonger conduction delay, which is indicative of the formation of atherapeutic lesion. For example, a continuous 50 cm transmural lesionthat creates a complete conduction block along its length will typicallyincrease the conduction delay to about 50 ms.

In some embodiments, a lesion can be tested at various points along itslength, one point at a time. The lesion may be tested with each of thestimulation and sensing electrode pairs that are adjacent to acoagulation electrode that was used to form a lesion. If for example,the proximal four coagulation electrodes are used to form a lesion, thenthe proximal four pairs of stimulation and sensing electrodes will beused, one stimulation/sensing at a time, to determine whether or not thelesion creating procedure created a complete conduction block. In somecases, if a pacing pulse is able to cross the lesion, the heart willbeat faster, for example 120 beats/minute. This may be determined byobservation or by use of an ECG machine that is monitoring the heart.Additional coagulation may be used to complete an incomplete lesion.Because muscle bundles are not always connected near the pulmonaryveins, it may be desirable to apply stimulation energy to a number oftissue areas to reduce the possibility of false negatives. Stimulationelectrodes may be used to monitor tissue within a region that wasintended to be isolated. In the context of pulmonary vein isolation, forexample, stimulation electrodes may be placed in contact with viabletissue on the pulmonary vein side of the lesion. Local activation withinthe isolated region from the heart's natural stimulation is indicativeof a gap in the lesion. Treatment assembly 1000 may be used to determinewhether or not a lesion is transmural. Tissue stimulation electrodes maybe connected to a tissue stimulation apparatus and used to providestimulation energy. Tissue stimulation electrodes may also be used forsensing local tissue activation. Stimulation electrodes may operate in abipolar mode, and also may operate in unipolar mode.

In some tissue treatment system or method embodiments, coagulationelectrodes can be configured to transmit RF energy. Optionally, othertypes of coagulation elements, such as such as lumens for chemicalablation, laser arrays, ultrasonic transducers, microwave electrodes,ohmically heated hot wires, and the like may be substituted for orsupplement the coagulation electrodes. Coagulation electrodes may bearranged as a series of spaced electrodes. Optionally, a single elongatecoagulation electrode may be employed. Coagulation electrodes can be inthe form of wound, spiral closed coils. The coils can be made ofelectrically conducting material, such as copper alloy, platinum, orstainless steel, or compositions such as drawn-filled tubing, forexample a copper core with a platinum jacket. The electricallyconducting material of the coils can be further coated withplatinum-iridium or gold to improve its conduction properties andbiocompatibility.

In the case of laser ablation, some versions include an end firing diodethat can be automatically moved so as to direct energy toward severaldistinct locations along a line or path. In some versions, a laser beamis transmitted down a control diffracting mechanism, and reflected alonga direction orthogonal to the longitudinal axis of the device. Hence,light can be dispersed in a uniform fashion along the diffractingmechanism. Laser ablation techniques according to embodiment of thepresent invention can involved these types of laser approaches, as wellas related techniques which are described in U.S. Pat. Nos. 6,071,302and 6,270,492, the contents of which are incorporated herein byreference.

Optionally, coagulation electrodes 1110 may be in the form of solidrings of conductive material, like platinum-iridium or gold, coated uponthe device using conventional coating techniques or an ion beam assisteddeposition (IBAD) process. For better adherence, an undercoating ofnickel, silver or titanium can be applied. The coagulation electrodescan also be in the form of helical ribbons. The electrodes can also beformed with a conductive ink compound that is pad printed onto anon-conductive tubular body. A conductive ink compound can include asilver-based flexible adhesive conductive ink (polyurethane binder),however other metal-based adhesive conductive inks such asplatinum-based, gold-based, copper-based, etc., may also be used to formelectrodes. Such inks may be more flexible than epoxy-based inks. Opencoil electrodes may also be employed for coagulation.

Exemplary flexible coagulation electrodes 1110 can be about 4 mm toabout 20 mm in length. In some embodiments, the electrodes are about12.5 mm in length with about 1 mm to about 3 mm spacing, which canresult in the creation of continuous lesion patterns in tissue whencoagulation energy is applied simultaneously from adjacent electrodesthrough tissue to an indifferent electrode. For rigid coagulationelectrodes, the length of each electrode can vary from about 2 mm toabout 10 mm. The diameter, whether flexible or rigid, will typically beabout 3 mm. For cardiovascular applications, the length will sometimesrange from between about 2 cm and 8 cm in those instances where power issupplied at both longitudinal ends of each electrode, and the end to endresistance is about 5 ohm to about 15 ohm. The diameter of theelectrodes may in some cases range from about 1.5 mm to about 3 mm forcardiovascular applications and, in some embodiments, the outer diameteris about 2 mm.

A tissue treatment system may include one or more temperature sensorswhich can help provide temperature readings and facilitate improvedtemperature control. As such, the actual tissue temperature cancorrespond to the temperature set by the physician on the power supplyand control device, thereby providing the physician with control of thelesion creation process and reducing the likelihood that embolicmaterials will be formed. A reference thermocouple may also be provided.

A power supply and control system can include an electrosurgical unit(ESU) that supplies and controls RF power. An ESU can be is capable ofsupplying and controlling power on an electrode-by-electrode basis, in a“multi-channel control.” An ESU can transmit energy to the coagulationelectrodes and receives signal from the temperature sensors via anysuitable connectivity. An ESU can be operable in a bipolar mode, wheretissue coagulation energy emitted by one of the coagulation electrodesis returned through one of the other coagulation electrodes, and aunipolar mode, where the tissue coagulation energy emitted by thecoagulation electrodes is returned through one or more indifferentelectrodes that are externally attached to the skin of the patient witha patch, or one or more electrodes that are positioned in the bloodpool, and a cable. It is also possible to supply power in a combinedbipolar/unipolar mode. An ESU can individually power and control eachcoagulation electrode 1110, optionally based on the hottest of the twomeasured temperatures at that particular electrode.

Embodiments of the present invention encompass tissue treatment systemsand methods for verifying electrical conduction block across ablationlesions and for verifying the effectiveness of an ablation procedure increating an electrical conduction block across the cardiac tissue. Anexemplary verification system includes a conduction block-verificationmechanism such as a pacing probe or electrode. A verification method caninvolve transmitting an electrical pulse to a patient tissue so as tostimulate the tissue. In some cases, the electrical pulse is applied ata rate higher than the intrinsic atrial or ventricular contraction rateor heart rate. A measurement of the pacing threshold, or the minimumvoltage or amperage required to excite the tissue, above the intrinsicexcitation rate, can be recorded or monitored prior to, during, andfollowing completion of one or more ablation lesions, which may be aimedto isolate specific regions of the heart.

In use, a tissue treatment system can be used to directly contact theepicardium of the heart and transmits electrical energy to electricallystimulate the heart. Such electrical energy can be delivered by a pulsegenerator that is coupled with or integral to the tissue treatmentsystem. In some cases, an operator can position the tissue treatmentsystem using direct or endoscopic visualization of the tissue surface.Optionally, an operator can monitor, verify, or evaluate a conductionblock with the assistance of an ECG recorders. A tissue treatment systemcan be configured to transmit electrical pacing pulses of variableamplitude up to 20 mA or 10 V in amplitude to pace the heart abovenormal sinus rhythm, optionally up to 200 BPM to the target anatomicalarea of the epicardium. A tissue treatment system may also be capable ofpassively transmitting electrical pulses from the heart to an ECGrecorder.

A tissue treatment method may include the temporary pacing of a portionof the heart, for example the left atrium, and the verification orevaluation of an electrical conduction block across one or more ablationlesions. Such methods can provide an indication of lesion continuity andelectrical isolation of one or more specific regions on the heart. Atissue treatment system can be used after creating a set of lesions onthe epicardium of the left atrium encircling the pulmonary veins inconjunction with surgical, interventional cardiology, orelectrophysiology treatments for atrial fibrillation to determine if orto what extent electrical conduction block is achieved.

A tissue treatment system can be used to pace the left atrium bycontacting the left atrium both inside and outside an encircling lesionaround the pulmonary veins. If significantly more voltage or current isrequired to pace the heart from inside the encircling lesion as opposedto outside, an inference of electrical isolation of the pulmonary veinscan be made. Exemplary methods can be used to assess electricalisolation of several regions of the heart across ablation lesions duringsurgical treatment of atrial fibrillation, open or minimally invasively,epicardially or endocardially. A pulse generator can supply a higherthan normal pacing rate and electrical impulse at variable amplitudes.The tissue treatment system can be used to contact the left atriumwithin the encircling lesion adjacent to the pulmonary veins and pacedto determine if electrical isolation or block was successful. If blockis not successful, then the impulse may be captured outside theencircling lesion and pacing of the entire heart may take place.

Embodiments of the present invention encompass tissue treatment systemsand methods that provide for the selective activation and deactivationof one or more stimulation or pacing electrodes, optionally based on anevaluation of the conduction block status of a patient tissue.Embodiments also encompass methods that involve determining oridentifying a set of one or more stimulation or pacing electrodes foractivation. Relatedly, embodiments also encompass methods that involvedetermining or identifying a set of one or more coagulation electrodesfor activation. In some cases, tissue treatment systems can beconfigured to activate one or more stimulation electrodes or coagulationelectrodes based on a determination of whether a treatment assembly ofthe tissue treatment system is in appropriate contact with the patienttissue. Relatedly, tissue treatment systems can be configured tomodulate the amount of energy transmitted by one or more stimulationelectrodes or coagulation electrodes based on a determination of whethera treatment assembly of the tissue treatment system is in appropriatecontact with the patient tissue. In some cases, tissue treatment systemscan be configured to activate one or more stimulation electrodes orcoagulation electrodes based on a determination or evaluation of theconduction block status of a patient tissue. For example, a method mayinvolve activating a coagulation electrode which is disposed at or neartissue not having a conduction block, and deactivating or not activatinga coagulation electrode which is disposed at or near tissue that has aconduction block. Optionally, tissue treatment systems can be configuredto modulate the amount of energy transmitted by one or more stimulationelectrodes or coagulation electrodes based on a determination orevaluation of the conduction block status of a patient tissue.Relatedly, a tissue treatment system can be configured to activate ordeactivate one or more stimulation electrodes or coagulation electrodesbased on a determination or evaluation of whether a treatment assemblyof the tissue treatment system is in appropriate contact with thepatient tissue and a determination or evaluation of the conduction blockstatus of a patient tissue. A tissue treatment system can also beconfigured to modulate the amount of energy transmitted by one or morestimulation electrodes or coagulation electrodes based on adetermination or evaluation of whether a treatment assembly of thetissue treatment system is in appropriate contact with the patienttissue and a determination or evaluation of the conduction block statusof a patient tissue.

According to some embodiments, tissue treatment system can be configuredto perform a conduction block test or evaluation during a coagulation orRF procedure, and to modulate the amount of coagulation or ablationenergy that is applied by the system to the patient's tissue. Forexample, a tissue treatment system can be configured to determine whenor where to initiate, increase, stop, or reduce power to one or morecoagulation electrodes of a treatment assembly based on a conductionblock analysis. Similarly, a tissue treatment system can be configuredto control when or where and in what amount energy is applied via one ormore coagulation electrodes of a treatment assembly based on aconduction block analysis. Often, such methods can involve determiningwhen to stop at least a portion of an ablation treatment. Relatedly,methods can involve stimulating a patient tissue to determine where aconduction block has been established, or at least partiallyestablished.

In some embodiments, a tissue treatment system can include or be inconnectivity with a coagulation energy generator, such as an RF energygenerator, which may include an integrated control mechanism formodulating the output of the generator based on the conduction blockstatus of a patient tissue. In some cases, a tissue treatment systemincludes a treatment assembly that is configured to apply a pacing orstimulation energy to the tissue via one or more coagulation electrodes.Standard ablation or coagulation electrodes are typically larger thanstandard stimulation electrodes, because ablation electrodes usuallydeliver greater amounts of current. Hence, stimulation of tissue with anablation electrode involves the application of more current than wouldotherwise be applied with a stimulation electrode. Generally,stimulation of tissue is initiated by a particular current density inthe tissue. Due to current dissipation in the tissue, as the surfacearea of an electrode is increased there is a corresponding proportionalincrease in the current to the electrode for stimulation. If there is aten fold increase in the electrode surface area, a ten fold increase inthe current amplitude is needed to achieve the current density requiredfor tissue stimulation (the voltage remains substantially unchanged). Inmany cases, the application of about 2 to 10 volts through an electrodeis sufficient to stimulate a tissue independent of electrode size, butthe required current is greater for larger electrodes.

In some embodiments, a coagulation electrode that is used to deliverstimulation energy can be configured to output 100 to 200 milliamps,while maintaining a compliance of 10 to 20 volts. In some cases, an RFelectrode can be configured to deliver energy at 460 kHz, which mayrequire a pacing circuit having a blocked return path. A two stage LCcircuit can be used for passive stimulation. Relatedly, a tissuetreatment system can have a first circuit for pacing and a secondcircuit for ablation, where the first and second circuits are isolatedfrom one another. In some cases, an LC circuit can be configured with alow impedance path at low frequencies used for pacing and a highimpedance at ablation frequencies.

Embodiments of the present invention also encompass a tissue treatmentsystem having an integrated ESU with a user interface that providesoutput signifying the status of one or more lesions. For example, a userinterface can identify or show where ablation is successful or wherethere is a gap in a linear lesion. Relatedly, a user interface can showelectrodes or otherwise provide a representation of one or moreelectrodes and their positioning at or near patient tissue. In somecases, a user interface can reconstruct a model of the heart to identifyareas of successful and unsuccessful ablation. Where a touch screen isused, the operator can touch the screen to identify where additionalablation attempts should be done.

An exemplary treatment method can include applying a first ablativeenergy to a first tissue location via a first electrode, and applying asecond ablative energy to a second tissue location via a secondelectrode. The method can also include performing a detection ormonitoring step before, during, or after applying the first and secondablative energies. The method can include detecting a subthresholdelectrical conductivity for the first tissue location and a thresholdelectrical conductivity for the second tissue location, anddiscontinuing or diminishing application of the first ablative energy tothe first tissue location while continuing application of the secondablative energy to the second tissue location. In a related embodiment,an exemplary treatment method includes activating one or morecoagulation electrodes of a treatment assembly, applying energy to apatient tissue with the activated coagulation electrodes, performing aconduction block or lesion pattern analysis of the patient tissue, andadjusting the activation level of one or more of the coagulationelectrodes based on the conduction block or lesion pattern analysis.

Embodiments also encompass selective deactivation methods using a tissuetreatment system. For example, a tissue treatment method can involveactivating one or more coagulation electrodes of a treatment assembly,continuing application of a first ablative energy to a first tissuelocation via a first ablation electrode, and discontinuing or reducingapplication of a second ablative energy to a second tissue location viaa second ablation electrode after detecting a conduction block at ornear the second tissue location. Similar embodiments involve operating atreatment assembly during a cardiac surgical procedure, evaluating aconduction block condition at a first tissue location, and discontinuingapplication of a first ablative energy to the first tissue location inresponse to the condition of the conduction block at the first tissuelocation, and continuing application of the second ablative energy tothe second tissue location, optionally in response to a conduction blockstatus of the second tissue location. Further, exemplary methods caninvolve operating an ablation assembly during a cardiac surgicalprocedure, evaluating a conduction block condition of a patient tissuetreatment site, and based on the evaluation of the conduction blockcondition, continuing application of a first ablative energy to a firsttissue location, and discontinuing or reducing application of a secondablative energy to a second tissue location.

Monopolar Ablation Technologies II

For monopolar ablation technologies with long linear electrodes, someembodiments involve using pairs of electrodes spaced more than about 2cm apart to apply the ablating voltage pulses. For example, withreference to FIG. 9 , electrodes 920 a and 920 b can be separated by adistance D, and distance D may be more than about 2 cm. In suchconfigurations, voltage pulses of 1500-3000 volts applied between thespaced-apart electrodes with pulse durations of 0.02-0.1 msec can besufficient to kill all or substantially all myocardial cells withinabout 5 mm of each of the electrodes. When it is desired that all orsubstantially all of the myocardial cells be irreversibly damaged by thehigh voltage gradients within the targeted tissue, 10-50 pulses can bedelivered over a 1 to 60 second time interval. For such electrodeconfigurations and voltage delivery methods, the region of tissuesubjected to lethal voltage fields can be determined by the amplitude ofthe applied pulses and the pulse width. For a 0.05 msec pulse width,multiple 1500 Volt pulses can be sufficient to ablate tissue to a depthof about 5 mm at each electrode. To achieve reliable lesions depths ofabout 10 mm, it may be useful to increase the voltage amplitude to about3000 volts. In tissue regions that are thick, for example about 10 mm,lesions typically will be also be wide, the lesion having approximatelya semicircular cross section. In thinner tissue regions, the lesionwidth typically will be thinner, being about twice as wide as the tissueis thick. In other words, the lesion will be about 8 mm wide where theatrial wall is about 4 mm thick.

Monopolar Ablation Technologies III

For monopolar ablation technologies with long linear electrodes, otherembodiments use one polarity for one electrode (A), and an oppositepolarity is applied to multiple similar sized electrodes (B), eachspaced more than about 2 cm apart from electrode (A) to apply theablating voltage pulses. For example, (A) and (B) electrodes can belinearly arranged as follows:

-   -   BBBBBABBBB    -   where the distance between the (A) electrode and each of the        two (B) electrodes adjacent to the (A) electrode is greater than        2 cm. In such configurations, voltage pulses of 1000-2000 volts        30 applied between the spaced-apart electrodes with pulse        durations of 0.02-0.1 msec typically are sufficient to kill all        or substantially all myocardial cells within about 5 mm of        electrode (A). When it is desired that all or substantially all        of the myocardial cells be irreversibly damaged by the high        voltage gradients within the targeted tissue, 5-50 pulses can be        delivered over a 1 to 60 second time interval. For such        electrode configurations and voltage delivery methods, the        region of tissue subjected to lethal voltage fields can be        determined by the amplitude of the applied pulses and the pulse        width. For a 0.05 msec pulse width, multiple 1000 Volt pulses        typically are sufficient to ablate tissue to a depth of about 5        mm at electrode (A). To achieve reliable lesions depths of about        10 mm at the electrode (A) location, it may be useful to        increase the voltage amplitude to about 2000 volts. In tissue        regions that are thick, for example about 10 mm, lesions        typically will be also be wide, the lesion having approximately        a semicircular cross section. In thinner tissue regions, the        lesion width typically will be thinner, being about twice as        wide as the tissue is thick. In other words, the lesion will be        about 8 mm wide where the atrial wall is about 4 mm thick.        Lesion depths at electrodes (B) locations usually will be less        than those produced at electrode (A) locations. In some        instances, the lesion depths at electrode (B) locations will be        lower than at electrode (A) locations, when three or more        electrodes (B) are used. In some cases, this ablation mode can        be carried out without the use of a surface return electrode,        while retaining the lower voltage pulse amplitudes involved with        ablating tissue.

Other Ablation Technologies

For ablation technologies with long linear electrodes, some embodimentsuse pairs of electrodes spaced about 4 mm to about 10 mm apart to applythe ablating voltage pulses. In exemplary embodiments, electrodes can beseparated by a distance similar to the tissue wall thickness. In suchcases, more than two electrodes can be so connected. FIG. 12 showsaspects of an ablation system 1200 according to embodiments of thepresent invention. Ablation system 1200 can include multiple electrodes1210 linearly mounted on a catheter shaft 1220. For example, system 1200can include ten electrodes linearly mounted on catheter shaft 1220. Insome instances, the odd numbered electrodes (e.g. 1, 3, 5, 7, and 9) canbe connected to one voltage polarity and the even numbered electrodes(e.g. 2, 4, 6, 8, and 10) can be connected to an opposite voltagepolarity. An atrial wall thickness is generally about 4 mm or more inpatients with atrial fibrillation. Hence, an exemplary edge-to-edgeseparation distance D between electrodes can be about 6 mm. In somecases, an electrode length L can be 1-2 times as long as the distancebetween electrodes. In such a configuration, voltage pulses of 1500-3000volts applied between the spaced-apart electrodes with pulse durationsof 0.02-0.1 msec typically are sufficient to kill all or substantiallyall myocardial cells within about 5 mm of each of the electrodes. Whenit is desired that all or substantially all of the myocardial cells beirreversibly damaged by the high voltage gradients within the targetedtissue, 5-50 pulses can be delivered over a 1 to 60 second timeinterval. For such electrode configurations and voltage deliverymethods, the region of tissue subjected to lethal voltage fields can bedetermined by the amplitude of the applied pulses and the pulse width.For a 0.05 msec pulse width, multiple 1500 volt pulses typically aresufficient to ablate tissue to a depth of about 5 mm at each electrode.To achieve reliable lesions depths of about 10 mm, it may be useful toincrease the voltage amplitude to about 3000 volts. In tissue regionsthat are thick, for example about 10 mm, lesions typically will be alsobe wide, the lesion having approximately a semicircular cross section.In thinner tissue regions, the lesion width typically will be thinner,being about twice as wide as the tissue is thick. In other words, thelesion will be about 8 mm wide where the atrial wall is about 4 mmthick. Electrode configurations such as those depicted in FIG. 12 arewell suited for use with the tissue treatment system shown in FIG. 7 ,as well as various suction-based lesion forming minimally invasiveablation probes.

Effects of Voltage Pulses on Heart Tissue

Short duration voltage pulses such as those described herein have atleast three different effects on myocardial tissues, depending on thelocal strength of the applied field or voltage gradient. Field strengthsabove 500V/cm damage myocytes and can be lethal when applied multipletimes. Tissue stunning can occur with single high-voltage pulses havingvoltage gradients above 500V/cm, with myocardial tissue beingunresponsive to stimulation for more than 30 seconds following thedelivered pulse. Stunning can also occur in myocardial tissue exposed tomultiple applied pulses producing gradients of 100-500V/cm in theaffected tissue. When a DC voltage pulse is used with the pulse durationof about 0.1 msec, tissue exposed to stimulation strengths of from about10 to 100 VI cm can be stimulated (paced) by the applied pulse. If onlyatrial tissue is so stimulated, such stimulation typically is not asafety issue, and may provide diagnostic information to the user of thisablation technology. However, if the field stimulation extends to theventricle, such stimulation can induce ventricular tachycardia or evenventricular fibrillation. This potential safety issue can be addressedeither by applying the voltage pulse synchronously with ventricularcontraction (during the QRS complex of the ECG) by applying a sequenceof higher frequency pulses instead of a single DC pulse, or by applyinga pulsed RF waveform.

Tissue Heating

When ablating tissue with high voltages, the pulse sequence is usuallydesigned to result in peak tissue temperatures of less than about 50° C.so that little or no thermally-induced tissue ablation occurs. Often, itis also useful to avoid creating tissue temperatures that exceed about65° C., which can coagulate the tissue and result in geometrical changesto the tissue structures both on a microscopic and visual scale.Coagulated tissue is typically more thrombogenic than tissue containingcells lethally injured by high-voltage pulses. Furthermore, healing isgenerally expected to proceed more rapidly because the non-cellularstructure of the heart is not modified by the voltage structure and someblood flow through the tissue would be maintained. The pulse sequencesgenerally described herein do not heat the ablated tissuessignificantly, according to tome embodiments. Even with the mostaggressive pulse sequences described (highest voltages, longest pulsedurations, and most pulse numbers), the total amount of heating is lessthan that typically provided by one second of RF ablation and less than1% of the energy needed to produce a thermally-based ablation lesion.

The lack of clear changes to the tissue appearance can result in errorsof producing overlapping lesions, which is commonly required for AFtherapies. One method which enables visualization of lesions involvescreating a local thermal injury after providing the fatal high-voltagepulse sequence through the application electrodes. For example, it ispossible to create such local visually apparent lesions with a shortpulse of RF power delivered for 3 seconds or less. For shortapplications of power to the tissues, the lesion volume typically isdetermined by the tissues directly heated and thermal expansion of thelesion is minimized. Optionally, high-voltage pulses with longer pulsedurations can be delivered to the tissues to provide a similar tissueheating.

Related Suction Stabilized Bipolar Embodiments

Aspects of high voltage pulse ablation as described herein are wellsuited for use in suction stabilized bipolar ablation systems andmethods. For example, suction stabilized bipolar techniques as describedin U.S. Provisional Patent Application No. 61/456,918, filed Nov. 12,2010 (Attorney Docket No. 021063-003800US), incorporated herein byreference, can be used to administer exemplary high voltage pulseablations. Optionally, such treatments may involve the use oftemperature sensors. In some cases, temperature sensing techniques canbe used in conjunction with a marking process.

Marking Techniques

Following the application of various high voltage pulse orradiofrequency energy ablation treatments, it may be difficult todirectly visualize or distinguish a lesion generated by the treatment.For example, the tissue surface may not be heated sufficiently to createa visible mark. Hence, a surgeon may not be able to see the lesion withthe unaided eye, without assistance from a magnifying or othervision-enhancing optical device. In these and other instances, it may bedesirable or helpful to create a mark or indicia on the tissue surfacewhich corresponds to the lesion.

In some cases, administration of radiofrequency energy can be used toform such markings. For example, radiofrequency energy can be applied soas to heat the tissue surface to a temperature of about 60° C. orgreater, which results in a visible mark that can be easily seen by asurgeon or operator. In some cases, certain high voltage pulse regimenscan be used to form such markings by purposefully heating the tissue.For example, such heating can be achieved by increasing the magnitude ofthe voltage pulse, or by increasing the width of the voltage pulse, thusforming a visible mark on the tissue surface. The delivered energyrequirement to locally increase temperatures to 60° C. so as to create avisible mark varies by electrode configuration but is typically about 10Joules/cm of electrode length. The energy can be delivered with severalpulses using temperature monitoring to the energy delivered. Since onlya surface mark is desired, the thermal marking energy should bedelivered in less than three seconds. Heating the tissue to temperatureshigher than 90° C. should be avoided, since such temperatures can dryout the tissue and interfere with any subsequent ablation attempts.

Accordingly, either a high voltage pulse ablation protocol or aradiofrequency energy ablation protocol may be performed to create alesion in the tissue, and either a high voltage pulse ablation protocolor a radiofrequency energy ablation protocol may be performed to createa mark on the tissue.

In some cases, marking may act to dry out the outer surface of thetissue, making it more resistive, and thus interfere with formation ofthe lesion.

In some cases, high voltage gradients can be used to make the transmurallesion, and even higher voltage gradients can be used to make thesurface mark. Relatedly, the high voltage gradients used to make thetransmural lesion may in some cases be more reliable than the evenhigher voltage gradients used to make the surface mark. According tosome embodiments, it may be easier to increase pulse width rather thanpulse voltage to thermally heat the tissue for marking. Higher voltagesmay provide more assured irreversible cellular damage, independent ofthermal effects.

According to some embodiments, a tissue surface mark can have a depthwithin a range from about 0.5 mm to about 3.0 mm. In some cases, atissue surface mark may be about 1 mm deep.

Individual system elements or aspects of a tissue treatment computersystem may be implemented in a separated or more integrated manner. Insome embodiments, treatment systems, which may include computer systems,also include software elements, for example located within a workingmemory of a memory, including an operating system and other code, suchas a program designed to implement method embodiments of the presentinvention. In some cases, software modules implementing thefunctionality of the methods as described herein, may be stored in astorage subsystem. It is appreciated that systems can be configured tocarry out various method aspects described herein. Each of the devicesor modules of the present invention can include software modules on acomputer readable medium that is processed by a processor, hardwaremodules, or any combination thereof. Any of a variety of commonly usedplatforms, such as Windows, Macintosh, and Unix, along with any of avariety of commonly used programming languages, such as C or C++, may beused to implement embodiments of the present invention. In some cases,tissue treatment systems include FDA validated operating systems orsoftware/hardware modules suitable for use in medical devices. Tissuetreatment systems can also include multiple operating systems. Forexample, a tissue treatment system can include a FDA validated operatingsystem for safety critical operations performed by the treatment system,such as data input, power control, diagnostic procedures, recording,decision making, and the like. A tissue treatment system can alsoinclude a non-validated operating system for less critical operations.In some embodiments, a computer system can be in integrated into atissue treatment system, and in some embodiments, a computer system canbe separate from, but in connectivity with, a tissue treatment system.It will be apparent to those skilled in the art that substantialvariations may be used in accordance with any specific requirements. Forexample, customized hardware might also be used and/or particularelements might be implemented in hardware, software (including portablesoftware, such as applets), or both. Further, connection to othercomputing devices such as network input/output devices may be employed.Relatedly, any of the hardware and software components discussed hereincan be integrated with or configured to interface with other medicaltreatment or information systems used at other locations.

While exemplary embodiments have been described in some detail, by wayof example and for clarity of understanding, those of skill in the artwill recognize that a variety of modification, adaptations, and changesmay be employed. Hence, the scope of the present invention should belimited solely by the claims.

We claim:
 1. A tissue treatment system configured to ablate a tissue,the system comprising: a clamp assembly comprising a first jaw mechanismand a second jaw mechanism configured to receive and compress a tissuetherebetween; a first electrode disposed on the first jaw mechanism andconfigured to contact the tissue; and a second electrode disposed on thesecond jaw mechanism and configured to contact the tissue; wherein thefirst electrode and the second electrode are configured so that at leastone of an ablation energy output of the first electrode and an ablationenergy output of the second electrode is automatically adjusted toaccommodate variable tissue thicknesses between the first electrode andthe second electrode.
 2. The system of claim 1, further comprising anactuator assembly operatively coupled to at least one of the first jawmechanism and the second jaw mechanism; and a coupling assemblyoperatively associated with the clamp assembly and the actuatorassembly.
 3. The system of claim 2, wherein the actuator assemblycomprises a plunger configured to open or close at least one of thefirst jaw mechanism and the second jaw mechanism.
 4. The system of claim2, wherein the coupling assembly comprises an elongate shaft.
 5. Thesystem of claim 1, wherein at least one of the first electrode or thesecond electrode is configured to ablate the tissue using radiofrequencyenergy.
 6. The system of claim 1, wherein at least one of the firstelectrode or the second electrode is configured to ablate the tissueusing high-voltage pulses.
 7. The system of claim 1, wherein the firstelectrode and the second electrode are configured to deliver bipolarenergy to the tissue.
 8. The system of claim 1, wherein at least one ofthe first electrode and the second electrode is configured to delivermonopolar energy to the tissue.
 9. The system of claim 1, wherein atleast one of the first electrode or the second electrode comprises aserpentine electrode.
 10. The system of claim 1, further comprising anelectrosurgical unit operatively associated with at least one of thefirst electrode and the second electrode; wherein the electrosurgicalunit is configured to supply and control at least one of the ablationenergy output of the first electrode or the ablation energy output ofthe second electrode.
 11. A method of ablating a tissue, the methodcomprising: compressing a target tissue between a first jaw comprising afirst electrode and a second jaw comprising a second electrode; ablatingthe target tissue by delivering ablation energy to the target tissue viaat least one of the first electrode and the second electrode, whereindelivering ablation energy to the target tissue comprises automaticallyindividually adjusting at least one of an ablation energy output of thefirst electrode and an ablation energy output of the second electrode toaccommodate variable tissue thicknesses between the first electrode andthe second electrode.
 12. The method of claim 11, wherein deliveringablation energy to the target tissue via at least one of the firstelectrode and the second electrode comprises applying a high voltagepulse regimen to the target tissue via at least one of the firstelectrode and the second electrode.
 13. The method of claim 12, whereinthe target tissue comprises a plurality of myocardial cells; and whereinthe high voltage pulse regimen is sufficient to irreversibly damage theplurality of myocardial cells.
 14. The method of claim 11, whereindelivering ablation energy to the target tissue via at least one of thefirst electrode and the second electrode comprises applyingradiofrequency energy to the target tissue via at least one of the firstelectrode and the second electrode.
 15. The method of claim 11, whereincompressing the target tissue comprises operating an actuator to move atleast one of the first jaw and the second jaw to close the first jaw andthe second jaw.
 16. The method of claim 11, wherein compressing thetarget tissue comprises closing the first jaw and the second jaw so thatthe first jaw and the second jaw are separated by less than about 5 mm.17. The method of claim 11, wherein automatically individually adjustingthe at least one of the ablation energy output of the first electrodeand the ablation energy output of the second electrode to accommodatevariable tissue thicknesses between the first electrode and the secondelectrode comprises adjusting at least one of the ablation energy outputof the first electrode and the ablation energy output of the secondelectrode to deliver high voltage pulses to the target tissue aboveabout 500 V/cm.
 18. The method of claim 17, delivering ablation energyto the target tissue via the at least one of the first electrode and thesecond electrode comprises delivering the high voltage pulses to thetarget tissue synchronously with ventricular contraction.
 19. The methodof claim 11, further comprising adhering at least one of the firstelectrode and the second electrode to the target tissue by applyingsuction.
 20. The method of claim 11, wherein delivering ablation energyto the target tissue via the at least one of the first electrode and thesecond electrode comprises delivering about 5-50 pulses at about1500-3000 V with pulse durations of about 0.02-0.1 ms over a timeinterval of about 1-60 s.
 21. The method of claim 11, further comprisingcreating a mark or indicia on a surface of the target tissuecorresponding to a lesion.